UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM N-CSR

CERTIFIED SHAREHOLDER REPORT OF REGISTERED

MANAGEMENT INVESTMENT COMPANIES

Investment Company Act file number 811-06481

Franklin Municipal Securities Trust

(Exact name of registrant as specified in charter)

One Franklin Parkway, San Mateo, CA 94403-1906

(Address of principal executive offices) (Zip code)

Alison Baur

Franklin Templeton

One Franklin Parkway

San Mateo, CA 94403-1906

(Name and address of agent for service)

Registrant’s telephone number, including area code: (650) 312-2000

Date of fiscal year end: February 28

Date of reporting period: February 28, 2026

(a) The Report to Shareholders is filed herewith

Franklin California High Yield Municipal Fund
Class A [FCQAX]
Annual Shareholder Report | February 28, 2026

This annual shareholder report contains important information about Franklin California High Yield Municipal Fund for the period March 1, 2025, to February 28, 2026.
You can find additional information about the Fund at https://www.franklintempleton.com/regulatory-fund-documents. You can also request this information by contacting us at (800) DIAL BEN/342-5236.  

WHAT WERE THE FUND COSTS FOR THE LAST YEAR? (based on a hypothetical $10,000 investment)

Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
Class A	$83	0.81%

HOW DID THE FUND PERFORM LAST YEAR AND WHAT AFFECTED ITS PERFORMANCE?

For the twelve months ended February 28, 2026, Class A shares of Franklin California High Yield Municipal Fund returned 3.74%. The Fund compares its performance to the Bloomberg Municipal Bond California Exempt Index, which returned 4.98% for the same period.

PERFORMANCE HIGHLIGHTS

Top contributors to performance:
↑	Selection in bonds with no external credit rating
↑	Underweight to bonds with 30 years to maturity
↑	Selection in B rated bonds

Top detractors from performance:
↓	Overweight to bonds with no external credit rating
↓	Overweight to bonds with 20 years to maturity
↓	Underweight bonds with 5 years or less to maturity

HOW DID THE FUND PERFORM OVER THE LAST 10 YEARS?

The Fund’s past performance is not necessarily an indication of how the Fund will perform in the future. The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares.

VALUE OF A $10,000 INVESTMENT ($9,625 AFTER MAXIMUM APPLICABLE SALES CHARGE) –
Class A 2/29/2016 — 2/28/2026

AVERAGE ANNUAL TOTAL RETURNS (%) Period Ended February 28, 2026

	1 Year	5 Year	10 Year
Class A	3.74	1.03	2.60
Class A (with sales charge)	-0.15	0.26	2.20
Bloomberg Municipal Bond Index	4.96	1.44	2.43
Bloomberg Municipal Bond California Exempt Index	4.98	1.45	2.37

Fund performance figures may reflect fee waivers and/or expense reimbursements, without which the performance would have been lower.

The Fund began offering Class A shares on 9/10/2018. Returns for periods before 9/10/2018, are based on the Fund’s Class A1 performance, which has been adjusted to take into account differences in class-specific operating expenses and maximum sales charges. For periods after the share class offering, performance for the specific share class is used, reflecting the applicable expenses and maximum sales charges.

Performance for periods prior to March 1, 2019, has been restated to reflect the current maximum sales charge, which is lower than the maximum sales charge prior to that date.

For current month-end performance, please call Franklin Templeton at (800) DIAL BEN/342-5236 or visit
https://www.franklintempleton.com/investments/options/mutual-funds.

Important data provider notices and terms available at www.franklintempletondatasources.com.

KEY FUND STATISTICS (as of February 28, 2026)

Total Net Assets	$3,281,260,262
Total Number of Portfolio Holdings	745
Total Management Fee Paid	$13,902,397
Portfolio Turnover Rate	13.89%

WHAT DID THE FUND INVEST IN? (as of February 28, 2026)

Portfolio Composition^* (% of Total Investments)

	WHERE CAN I FIND ADDITIONAL INFORMATION ABOUT THE FUND?
	Additional information is available on https://www.franklintempleton.com/regulatory-fund-documents, including its:
	• prospectus • proxy voting information • financial information • holdings • tax information

HOUSEHOLDING

You will receive the Fund’s shareholder reports every six months. In addition, you will receive an annual updated summary prospectus (detail prospectus available upon request). To reduce Fund expenses, we try to identify related shareholders in a household and send only one copy of the shareholder reports and summary prospectus. This process, called “householding,” will continue indefinitely unless you instruct us otherwise. If you prefer not to have these documents householded, please call us at (800) DIAL BEN/342-5236. At any time, you may view current prospectuses/summary prospectuses and shareholder reports on our website. If you choose, you may receive these documents through electronic delivery.

Franklin California High Yield Municipal Fund
Class A1 [FCAMX]
Annual Shareholder Report | February 28, 2026

This annual shareholder report contains important information about Franklin California High Yield Municipal Fund for the period March 1, 2025, to February 28, 2026.
You can find additional information about the Fund at https://www.franklintempleton.com/regulatory-fund-documents. You can also request this information by contacting us at (800) DIAL BEN/342-5236.  

WHAT WERE THE FUND COSTS FOR THE LAST YEAR? (based on a hypothetical $10,000 investment)

Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
Class A1	$67	0.66%

HOW DID THE FUND PERFORM LAST YEAR AND WHAT AFFECTED ITS PERFORMANCE?

For the twelve months ended February 28, 2026, Class A1 shares of Franklin California High Yield Municipal Fund returned 3.91%. The Fund compares its performance to the Bloomberg Municipal Bond California Exempt Index, which returned 4.98% for the same period.

PERFORMANCE HIGHLIGHTS

Top contributors to performance:
↑	Selection in bonds with no external credit rating
↑	Underweight to bonds with 30 years to maturity
↑	Selection in B rated bonds

Top detractors from performance:
↓	Overweight to bonds with no external credit rating
↓	Overweight to bonds with 20 years to maturity
↓	Underweight bonds with 5 years or less to maturity

HOW DID THE FUND PERFORM OVER THE LAST 10 YEARS?

The Fund’s past performance is not necessarily an indication of how the Fund will perform in the future. The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares.

VALUE OF A $10,000 INVESTMENT ($9,625 AFTER MAXIMUM APPLICABLE SALES CHARGE) –
Class A1 2/29/2016 — 2/28/2026

AVERAGE ANNUAL TOTAL RETURNS (%) Period Ended February 28, 2026

	1 Year	5 Year	10 Year
Class A1	3.91	1.18	2.70
Class A1 (with sales charge)	-0.04	0.41	2.31
Bloomberg Municipal Bond Index	4.96	1.44	2.43
Bloomberg Municipal Bond California Exempt Index	4.98	1.45	2.37

Fund performance figures may reflect fee waivers and/or expense reimbursements, without which the performance would have been lower.

Effective 9/10/18, Class A shares closed to new investors, were renamed Class A1 shares, and a new Class A share with a different expense structure became available.

Performance for periods prior to March 1, 2019, has been restated to reflect the current maximum sales charge, which is lower than the maximum sales charge prior to that date.

For current month-end performance, please call Franklin Templeton at (800) DIAL BEN/342-5236 or visit
https://www.franklintempleton.com/investments/options/mutual-funds.

Important data provider notices and terms available at www.franklintempletondatasources.com.

KEY FUND STATISTICS (as of February 28, 2026)

Total Net Assets	$3,281,260,262
Total Number of Portfolio Holdings	745
Total Management Fee Paid	$13,902,397
Portfolio Turnover Rate	13.89%

WHAT DID THE FUND INVEST IN? (as of February 28, 2026)

Portfolio Composition^* (% of Total Investments)

	WHERE CAN I FIND ADDITIONAL INFORMATION ABOUT THE FUND?
	Additional information is available on https://www.franklintempleton.com/regulatory-fund-documents, including its:
	• prospectus • proxy voting information • financial information • holdings • tax information

HOUSEHOLDING

You will receive the Fund’s shareholder reports every six months. In addition, you will receive an annual updated summary prospectus (detail prospectus available upon request). To reduce Fund expenses, we try to identify related shareholders in a household and send only one copy of the shareholder reports and summary prospectus. This process, called “householding,” will continue indefinitely unless you instruct us otherwise. If you prefer not to have these documents householded, please call us at (800) DIAL BEN/342-5236. At any time, you may view current prospectuses/summary prospectuses and shareholder reports on our website. If you choose, you may receive these documents through electronic delivery.

Franklin California High Yield Municipal Fund
Class C [FCAHX]
Annual Shareholder Report | February 28, 2026

This annual shareholder report contains important information about Franklin California High Yield Municipal Fund for the period March 1, 2025, to February 28, 2026.
You can find additional information about the Fund at https://www.franklintempleton.com/regulatory-fund-documents. You can also request this information by contacting us at (800) DIAL BEN/342-5236.  

WHAT WERE THE FUND COSTS FOR THE LAST YEAR? (based on a hypothetical $10,000 investment)

Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
Class C	$122	1.20%

HOW DID THE FUND PERFORM LAST YEAR AND WHAT AFFECTED ITS PERFORMANCE?

For the twelve months ended February 28, 2026, Class C shares of Franklin California High Yield Municipal Fund returned 3.20%. The Fund compares its performance to the Bloomberg Municipal Bond California Exempt Index, which returned 4.98% for the same period.

PERFORMANCE HIGHLIGHTS

Top contributors to performance:
↑	Selection in bonds with no external credit rating
↑	Underweight to bonds with 30 years to maturity
↑	Selection in B rated bonds

Top detractors from performance:
↓	Overweight to bonds with no external credit rating
↓	Overweight to bonds with 20 years to maturity
↓	Underweight bonds with 5 years or less to maturity

HOW DID THE FUND PERFORM OVER THE LAST 10 YEARS?

The Fund’s past performance is not necessarily an indication of how the Fund will perform in the future. The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares.

VALUE OF A $10,000 INVESTMENT – Class C 2/29/2016 — 2/28/2026

AVERAGE ANNUAL TOTAL RETURNS (%) Period Ended February 28, 2026

	1 Year	5 Year	10 Year
Class C	3.20	0.58	2.11
Class C (with sales charge)	2.21	0.58	2.11
Bloomberg Municipal Bond Index	4.96	1.44	2.43
Bloomberg Municipal Bond California Exempt Index	4.98	1.45	2.37

Fund performance figures may reflect fee waivers and/or expense reimbursements, without which the performance would have been lower.

For current month-end performance, please call Franklin Templeton at (800) DIAL BEN/342-5236 or visit
https://www.franklintempleton.com/investments/options/mutual-funds.

Important data provider notices and terms available at www.franklintempletondatasources.com.

KEY FUND STATISTICS (as of February 28, 2026)

Total Net Assets	$3,281,260,262
Total Number of Portfolio Holdings	745
Total Management Fee Paid	$13,902,397
Portfolio Turnover Rate	13.89%

WHAT DID THE FUND INVEST IN? (as of February 28, 2026)

Portfolio Composition^* (% of Total Investments)

	WHERE CAN I FIND ADDITIONAL INFORMATION ABOUT THE FUND?
	Additional information is available on https://www.franklintempleton.com/regulatory-fund-documents, including its:
	• prospectus • proxy voting information • financial information • holdings • tax information

HOUSEHOLDING

You will receive the Fund’s shareholder reports every six months. In addition, you will receive an annual updated summary prospectus (detail prospectus available upon request). To reduce Fund expenses, we try to identify related shareholders in a household and send only one copy of the shareholder reports and summary prospectus. This process, called “householding,” will continue indefinitely unless you instruct us otherwise. If you prefer not to have these documents householded, please call us at (800) DIAL BEN/342-5236. At any time, you may view current prospectuses/summary prospectuses and shareholder reports on our website. If you choose, you may receive these documents through electronic delivery.

Franklin California High Yield Municipal Fund
Class R6 [FCAQX]
Annual Shareholder Report | February 28, 2026

This annual shareholder report contains important information about Franklin California High Yield Municipal Fund for the period March 1, 2025, to February 28, 2026.
You can find additional information about the Fund at https://www.franklintempleton.com/regulatory-fund-documents. You can also request this information by contacting us at (800) DIAL BEN/342-5236.  

WHAT WERE THE FUND COSTS FOR THE LAST YEAR? (based on a hypothetical $10,000 investment)

Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
Class R6	$52	0.51%

HOW DID THE FUND PERFORM LAST YEAR AND WHAT AFFECTED ITS PERFORMANCE?

For the twelve months ended February 28, 2026, Class R6 shares of Franklin California High Yield Municipal Fund returned 4.05%. The Fund compares its performance to the Bloomberg Municipal Bond California Exempt Index, which returned 4.98% for the same period.

PERFORMANCE HIGHLIGHTS

Top contributors to performance:
↑	Selection in bonds with no external credit rating
↑	Underweight to bonds with 30 years to maturity
↑	Selection in B rated bonds

Top detractors from performance:
↓	Overweight to bonds with no external credit rating
↓	Overweight to bonds with 20 years to maturity
↓	Underweight bonds with 5 years or less to maturity

HOW DID THE FUND PERFORM OVER THE LAST 10 YEARS?

The Fund’s past performance is not necessarily an indication of how the Fund will perform in the future. The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares.

VALUE OF A $10,000 INVESTMENT – Class R6 2/29/2016 — 2/28/2026

AVERAGE ANNUAL TOTAL RETURNS (%) Period Ended February 28, 2026

	1 Year	5 Year	10 Year
Class R6	4.05	1.30	2.83
Bloomberg Municipal Bond Index	4.96	1.44	2.43
Bloomberg Municipal Bond California Exempt Index	4.98	1.45	2.37

Fund performance figures may reflect fee waivers and/or expense reimbursements, without which the performance would have been lower.

The Fund began offering Class R6 shares on 8/1/2017. Returns for periods before 8/1/2017, are based on the Fund’s Advisor Class performance, which has been adjusted to take into account differences in class-specific operating expenses and maximum sales charges. For periods after the share class offering, performance for the specific share class is used, reflecting the applicable expenses and maximum sales charges.

For current month-end performance, please call Franklin Templeton at (800) DIAL BEN/342-5236 or visit
https://www.franklintempleton.com/investments/options/mutual-funds.

Important data provider notices and terms available at www.franklintempletondatasources.com.

KEY FUND STATISTICS (as of February 28, 2026)

Total Net Assets	$3,281,260,262
Total Number of Portfolio Holdings	745
Total Management Fee Paid	$13,902,397
Portfolio Turnover Rate	13.89%

WHAT DID THE FUND INVEST IN? (as of February 28, 2026)

Portfolio Composition^* (% of Total Investments)

	WHERE CAN I FIND ADDITIONAL INFORMATION ABOUT THE FUND?
	Additional information is available on https://www.franklintempleton.com/regulatory-fund-documents, including its:
	• prospectus • proxy voting information • financial information • holdings • tax information

HOUSEHOLDING

You will receive the Fund’s shareholder reports every six months. In addition, you will receive an annual updated summary prospectus (detail prospectus available upon request). To reduce Fund expenses, we try to identify related shareholders in a household and send only one copy of the shareholder reports and summary prospectus. This process, called “householding,” will continue indefinitely unless you instruct us otherwise. If you prefer not to have these documents householded, please call us at (800) DIAL BEN/342-5236. At any time, you may view current prospectuses/summary prospectuses and shareholder reports on our website. If you choose, you may receive these documents through electronic delivery.

Franklin California High Yield Municipal Fund
Advisor Class [FVCAX]
Annual Shareholder Report | February 28, 2026

This annual shareholder report contains important information about Franklin California High Yield Municipal Fund for the period March 1, 2025, to February 28, 2026.
You can find additional information about the Fund at https://www.franklintempleton.com/regulatory-fund-documents. You can also request this information by contacting us at (800) DIAL BEN/342-5236.  

WHAT WERE THE FUND COSTS FOR THE LAST YEAR? (based on a hypothetical $10,000 investment)

Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
Advisor Class	$57	0.56%

HOW DID THE FUND PERFORM LAST YEAR AND WHAT AFFECTED ITS PERFORMANCE?

For the twelve months ended February 28, 2026, Advisor Class shares of Franklin California High Yield Municipal Fund returned 4.00%. The Fund compares its performance to the Bloomberg Municipal Bond California Exempt Index, which returned 4.98% for the same period.

PERFORMANCE HIGHLIGHTS

Top contributors to performance:
↑	Selection in bonds with no external credit rating
↑	Underweight to bonds with 30 years to maturity
↑	Selection in B rated bonds

Top detractors from performance:
↓	Overweight to bonds with no external credit rating
↓	Overweight to bonds with 20 years to maturity
↓	Underweight bonds with 5 years or less to maturity

HOW DID THE FUND PERFORM OVER THE LAST 10 YEARS?

The Fund’s past performance is not necessarily an indication of how the Fund will perform in the future. The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares.

VALUE OF A $10,000 INVESTMENT – Advisor Class 2/29/2016 — 2/28/2026

AVERAGE ANNUAL TOTAL RETURNS (%) Period Ended February 28, 2026

	1 Year	5 Year	10 Year
Advisor Class	4.00	1.28	2.79
Bloomberg Municipal Bond Index	4.96	1.44	2.43
Bloomberg Municipal Bond California Exempt Index	4.98	1.45	2.37

Fund performance figures may reflect fee waivers and/or expense reimbursements, without which the performance would have been lower.

For current month-end performance, please call Franklin Templeton at (800) DIAL BEN/342-5236 or visit
https://www.franklintempleton.com/investments/options/mutual-funds.

Important data provider notices and terms available at www.franklintempletondatasources.com.

KEY FUND STATISTICS (as of February 28, 2026)

Total Net Assets	$3,281,260,262
Total Number of Portfolio Holdings	745
Total Management Fee Paid	$13,902,397
Portfolio Turnover Rate	13.89%

WHAT DID THE FUND INVEST IN? (as of February 28, 2026)

Portfolio Composition^* (% of Total Investments)

	WHERE CAN I FIND ADDITIONAL INFORMATION ABOUT THE FUND?
	Additional information is available on https://www.franklintempleton.com/regulatory-fund-documents, including its:
	• prospectus • proxy voting information • financial information • holdings • tax information

HOUSEHOLDING

You will receive the Fund’s shareholder reports every six months. In addition, you will receive an annual updated summary prospectus (detail prospectus available upon request). To reduce Fund expenses, we try to identify related shareholders in a household and send only one copy of the shareholder reports and summary prospectus. This process, called “householding,” will continue indefinitely unless you instruct us otherwise. If you prefer not to have these documents householded, please call us at (800) DIAL BEN/342-5236. At any time, you may view current prospectuses/summary prospectuses and shareholder reports on our website. If you choose, you may receive these documents through electronic delivery.

(b) Not applicable

(a) The Registrant has adopted a code of ethics that applies to its principal executive officers and principal financial and accounting officer.

(c) N/A

(d) N/A

(f) Pursuant to Item 19(a) (1), the Registrant is attaching as an exhibit a copy of its code of ethics that applies to its principal executive officers and principal financial and accounting officer

The Board of Trustees of the Registrant has determined that Mary C. Choksi, possesses the technical attributes identified in Item 3 to Form N-CSR to qualify as an “audit committee financial expert,” and has designated Mary C. Choksi as the Audit Committee’s financial expert. Mary C. Choksi is an “independent” Trustee pursuant to paragraph (a)(2) of Item 3 to Form N-CSR.

Under applicable securities laws, a person determined to be an audit committee financial expert will not be deemed an “expert” for any purpose, including without limitation for the purposes of Section 11 of the Securities Act of 1933, as a result of being designated or identified as an audit committee financial expert. The designation or identification of a person as an audit committee financial expert does not impose on such person any duties, obligations, or liabilities greater than the duties, obligations, and liabilities imposed on such person as a member of the audit committee and board of directors in the absence of such designation or identification. The designation or identification of a person as an audit committee financial expert does not affect the duties, obligations, or liability of any other member of the audit committee or board of directors.

a) Audit Fees. The aggregate fees billed in the last two fiscal years ending February 28, 2025 and February 28, 2026 (the “Reporting Periods”) for professional services rendered by the Registrant’s principal accountant (the “Auditor”) for the audit of the Registrant’s annual financial statements, or services that are normally provided by the Auditor in connection with the statutory and regulatory filings or engagements for the Reporting Periods, were $50,486 in February 28, 2025 and $48,542 in February 28, 2026.

b) Audit-Related Fees. The aggregate fees billed in the Reporting Periods for assurance and related services by the Auditor that are reasonably related to the performance of the Registrant’s financial statements were $0 in February 28, 2025 and $0 in February 28, 2026.

(c) Tax Fees. The aggregate fees billed in the Reporting Periods for professional services rendered by the Auditor for tax compliance, tax advice and tax planning (“Tax Services”) were $10,000 in February 28, 2025 and $10,000 in February 28, 2026. These services consisted of (i) review or preparation of U.S. federal, state, local and excise tax returns; (ii) U.S. federal, state and local tax planning, advice and assistance regarding statutory, regulatory or administrative developments, and (iii) tax advice regarding tax qualification matters and/or treatment of various financial instruments held or proposed to be acquired or held.

There were no fees billed for tax services by the Registrant’s investment adviser and any entity controlling, controlled by, or under common control with the investment adviser that provides ongoing services to the Registrant (“Service Affiliates”) during the Reporting Periods that required pre-approval by the Audit Committee.

(d) All Other Fees. The aggregate fees billed in the Reporting Periods for products and services provided by the Auditor to the Registrant, other than the services reported in paragraphs (a) through (c) of this item, were $0 in February 28, 2025 and $0 in February 28, 2026.

There were no other non-audit services rendered by the Auditor to the Service Affiliates requiring pre-approval by the Audit Committee in the Reporting Periods.

(e) Audit Committee’s pre–approval policies and procedures described in paragraph (c) (7) of Rule 2-01 of Regulation S-X.

(1) The Registrant’s Audit Committee is directly responsible for approving the services to be provided by the Auditors, including:

(i) pre-approval of all audit and audit related services;

(ii) pre-approval of all non-audit related services to be provided to the Registrant by the Auditors;

(iii) pre-approval of all non-audit related services to be provided by the Auditors to the Registrant and the Service Affiliates where the non-audit services relate directly to the operations or financial reporting of the Registrant; and

(iv) establishment by the Audit Committee, if deemed necessary or appropriate, as an alternative to committee pre-approval of services to be provided by the Auditors, as required by paragraphs (ii) and (iii) above, of policies and procedures to permit such services to be pre-approved by other means, such as through establishment of guidelines or by action of a designated member or members of the committee; provided the policies and procedures are detailed as to the particular service and the committee is informed of each service and such policies and procedures do not include delegation of Audit Committee responsibilities, as contemplated under the Securities Exchange Act of 1934, to management; subject, in the case of (ii) through (iv), to any waivers, exceptions or exemptions that may be available under applicable law or rules.

(2) None of the services described in paragraphs (b) through (d) of this Item were performed in reliance on paragraph (c)(7)(i)(C) of Rule 2-01 of Regulation S-X.

(f) Not applicable.

(g) Non-audit fees billed by the Auditor for services rendered to the Registrant and the Service Affiliates during the reporting period were $489,326 in February 28, 2025 and $1,690,011 in February 28, 2026.

(h) Yes. The Registrant’s Audit Committee has considered whether the provision of non-audit services that were rendered to Service Affiliates, which were not pre-approved (not requiring pre-approval), is compatible with maintaining the Auditor’s independence. All services provided by the Auditor to the Registrant or to the Service Affiliates, which were required to be pre-approved, were pre-approved as required.

(i) Not applicable.

(j) Not applicable.

Not applicable.