EX-99.CERT

                           MFS MUNICIPAL SERIES TRUST

         CERTIFICATION PURSUANT TO SECTION 302 OF THE SARBANES-OXLEY ACT

I, Maria F. Dwyer, certify that:

1. I have reviewed this report on Form N-CSR of MFS Municipal Series Trust;

2. Based on my knowledge, this report does not contain any untrue statement of
   a material fact or omit to state a material fact necessary to make the
   statements made, in light of the circumstances under which such statements
   were made, not misleading with respect to the period covered by this report;

3. Based on my knowledge, the financial statements, and other financial
   information included in this report, fairly present in all material respects
   the financial condition, results of operations, changes in net assets, and
   cash flows (if the financial statements are required to include a statement
   of cash flows) of the registrant as of, and for, the periods presented in
   this report;

4. The registrant's other certifying officers and I are responsible for
   establishing and maintaining disclosure controls and procedures (as defined
   in Rule 30a-3(c) under the Investment Company Act of 1940) and internal
   control over financial reporting (as defined in Rule 30a-3(d) under the
   Investment Company Act of 1940) for the registrant and have:

     a. designed such disclosure controls and procedures, or caused such
        disclosure controls and procedures to be designed under our
        supervision, to ensure that material information relating to the
        registrant, including its consolidated subsidiaries, is made known to
        us by others within those entities, particularly during the period in
        which this report is being prepared;

     b. designed such internal control over financial reporting, or caused such
        internal control over financial reporting to be designed under our
        supervision, to provide reasonable assurance regarding the reliability
        of financial reporting and the preparation of financial statements for
        external purposes in accordance with generally accepted accounting
        principles;

     c. evaluated the effectiveness of the registrant's disclosure controls and
        procedures and presented in this report our conclusions about the
        effectiveness of the disclosure controls and procedures as of a date
        within 90 days prior to the filing date of this report based on such
        evaluation; and

     d. disclosed in this report any change in the registrant's internal
        control over financial reporting that occurred during the second fiscal
        quarter of the period covered by the report that has materially
        affected, or is reasonably likely to materially affect, the
        registrant's internal control over financial reporting; and

5. The registrant's other certifying officers and I have disclosed to the
   registrant's auditors and the audit committee of the registrant's board of
   directors (or persons performing the equivalent functions):

     a. all significant deficiencies and material weaknesses in the design or
        operation of internal control over financial reporting which are
        reasonably likely to adversely affect the registrant's ability to
        record, process, summarize, and report financial information; and

     b. any fraud, whether or not material, that involves management or other
        employees who have a significant role in the registrant's internal
        control over financial reporting.


Date: May 24, 2005                   MARIA F. DWYER
      ------------                   ------------------------------------------
                                     Maria F. Dwyer
                                     Treasurer (Principal Financial Officer
                                     and Accounting Officer)


                                                                     EX-99.CERT

                           MFS MUNICIPAL SERIES TRUST

         CERTIFICATION PURSUANT TO SECTION 302 OF THE SARBANES-OXLEY ACT

I, Robert J. Manning, certify that:

1. I have reviewed this report on Form N-CSR of MFS Municipal Series Trust;

2. Based on my knowledge, this report does not contain any untrue statement of
   a material fact or omit to state a material fact necessary to make the
   statements made, in light of the circumstances under which such statements
   were made, not misleading with respect to the period covered by this report;

3. Based on my knowledge, the financial statements, and other financial
   information included in this report, fairly present in all material respects
   the financial condition, results of operations, changes in net assets, and
   cash flows (if the financial statements are required to include a statement
   of cash flows) of the registrant as of, and for, the periods presented in
   this report;

4. The registrant's other certifying officers and I are responsible for
   establishing and maintaining disclosure controls and procedures (as defined
   in Rule 30a-3(c) under the Investment Company Act of 1940) and internal
   control over financial reporting (as defined in Rule 30a-3(d) under the
   Investment Company Act of 1940) for the registrant and have:

     a. designed such disclosure controls and procedures, or caused such
        disclosure controls and procedures to be designed under our
        supervision, to ensure that material information relating to the
        registrant, including its consolidated subsidiaries, is made known to
        us by others within those entities, particularly during the period in
        which this report is being prepared;

     b. designed such internal control over financial reporting, or caused such
        internal control over financial reporting to be designed under our
        supervision, to provide reasonable assurance regarding the reliability
        of financial reporting and the preparation of financial statements for
        external purposes in accordance with generally accepted accounting
        principles;

     c. evaluated the effectiveness of the registrant's disclosure controls and
        procedures and presented in this report our conclusions about the
        effectiveness of the disclosure controls and procedures as of a date
        within 90 days prior to the filing date of this report based on such
        evaluation; and

     d. disclosed in this report any change in the registrant's internal
        control over financial reporting that occurred during the second fiscal
        quarter of the period covered by the report that has materially
        affected, or is reasonably likely to materially affect, the
        registrant's internal control over financial reporting; and

5. The registrant's other certifying officers and I have disclosed to the
   registrant's auditors and the audit committee of the registrant's board of
   directors (or persons performing the equivalent functions):

     a. all significant deficiencies and material weaknesses in the design or
        operation of internal control over financial reporting which are
        reasonably likely to adversely affect the registrant's ability to
        record, process, summarize, and report financial information; and

     b. any fraud, whether or not material, that involves management or other
        employees who have a significant role in the registrant's internal
        control over financial reporting.


Date: May 24, 2005                   ROBERT J. MANNING
      ------------                   ---------------------------------------
                                     Robert J. Manning
                                     President (Principal Executive Officer)

                                                                  EX-99.906CERT

                           MFS MUNICIPAL SERIES TRUST

         CERTIFICATION PURSUANT TO SECTION 906 OF THE SARBANES-OXLEY ACT

I, Maria F. Dwyer, certify that, to my knowledge:

1. The Form N-CSR (the "Report") of MFS Municipal Series Trust (the
   "Registrant") fully complies for the period covered by the Report with the
   requirements of Section 13(a) or 15(d) of the Securities Exchange Act of
   1934; and

2. The information contained in the Report fairly presents, in all material
   respects, the financial condition and results of operations of the
   Registrant.


Date: May 24, 2005                   MARIA F. DWYER
      ------------                   ------------------------------------------
                                     Maria F. Dwyer
                                     Treasurer (Principal Financial Officer
                                     and Accounting Officer)


A SIGNED ORIGINAL OF THIS WRITTEN STATEMENT REQUIRED BY SECTION 906 HAS BEEN
PROVIDED TO THE REGISTRANT AND WILL BE RETAINED BY THE REGISTRANT AND FURNISHED
TO THE SECURITIES AND EXCHANGE COMMISSION OR ITS STAFF UPON REQUEST.

                                                                   EX-99.906CERT

                           MFS MUNICIPAL SERIES TRUST

         CERTIFICATION PURSUANT TO SECTION 906 OF THE SARBANES-OXLEY ACT

I, Robert J. Manning, certify that, to my knowledge:

1. The Form N-CSR (the "Report") of MFS Municipal Series Trust (the
   "Registrant") fully complies for the period covered by the Report with the
   requirements of Section 13(a) or 15(d) of the Securities Exchange Act of
   1934; and

2. The information contained in the Report fairly presents, in all material
   respects, the financial condition and results of operations of the
   Registrant.


Date: May 24, 2005                   ROBERT J. MANNING
      ------------                   ------------------------------------------
                                     Robert J. Manning
                                     President (Principal Executive Officer)


A SIGNED ORIGINAL OF THIS WRITTEN STATEMENT REQUIRED BY SECTION 906 HAS BEEN
PROVIDED TO THE REGISTRANT AND WILL BE RETAINED BY THE REGISTRANT AND FURNISHED
TO THE SECURITIES AND EXCHANGE COMMISSION OR ITS STAFF UPON REQUEST.