REPORT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

To the Board of Trustees of MFS Municipal Series Trust and
the Shareholders of MFS Alabama Municipal Bond Fund, MFS
Arkansas Municipal Bond Fund, MFS California Municipal Bond
Fund, MFS Georgia Municipal Bond Fund, MFS Maryland Municipal
Bond Fund, MFS Massachusetts Municipal Bond Fund, MFS Mississippi
Municipal Bond Fund, MFS New York Municipal Bond Fund, MFS North
Carolina Municipal Bond Fund, MFS Pennsylvania Municipal Bond
Fund, MFS South Carolina Municipal Bond Fund, MFS Municipal
Intermediate Fund, MFS Virginia Municipal Bond Fund, MFS West
Virginia Municipal Bond Fund and MFS Municipal Income Fund:

In planning and performing our audits of the financial statements
of MFS Alabama Municipal Bond Fund, MFS Arkansas Municipal Bond
Fund, MFS California Municipal Bond Fund, MFS Georgia Municipal
Bond Fund, MFS Maryland Municipal Bond Fund, MFS Massachusetts
Municipal Bond Fund, MFS Mississippi Municipal Bond Fund, MFS
New York Municipal Bond Fund, MFS North Carolina Municipal Bond
Fund, MFS Pennsylvania Municipal Bond Fund, MFS South Carolina
Municipal Bond Fund, MFS Municipal Intermediate Fund, MFS Virginia
Municipal Bond Fund, MFS West Virginia Municipal Bond Fund and MFS
Municipal Income Fund (collectively the "Funds") (each a series of
MFS Municipal Series Trust) as of and for the year ended March
31, 2024, in accordance with the standards of the Public Company
Accounting Oversight Board (United States), we considered the Funds'
internal control over financial reporting, including controls over
safeguarding securities, as a basis for designing our auditing
procedures for the purpose of expressing our opinions on the financial
statements and to comply with the requirements of Form N-CEN,
but not for the purpose of expressing an opinion on the effectiveness
of the Funds' internal control over financial reporting. Accordingly,
we express no such opinion.

The management of the Funds is responsible for establishing and
maintaining effective internal control over financial reporting.
In fulfilling this responsibility, estimates and judgments by
management are required to assess the expected benefits and related
costs of controls. A fund's internal control over financial reporting
is a process designed 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. A fund's internal control over financial reporting
includes those policies and procedures that (1) pertain to the
maintenance of records that, in reasonable detail, accurately and fairly
reflect the transactions and dispositions of the assets of the fund;
(2) provide reasonable assurance that transactions are recorded as
necessary to permit preparation of financial statements in accordance
with generally accepted accounting principles, and that receipts and
expenditures of the fund are being made only in accordance with
authorizations of management of the fund and trustees of the
trust; and (3) provide reasonable assurance regarding prevention
or timely detection of unauthorized acquisition, use, or disposition
of a fund's assets that could have a material effect on the financial
statements.

Because of its inherent limitations, internal control over financial
reporting may not prevent or detect misstatements. Also, projections
of any evaluation of effectiveness to future periods are subject to
the risk that controls may become inadequate because of changes in
conditions or that the degree of compliance with the policies or
procedures may deteriorate.

A deficiency in internal control over financial reporting exists when
the design or operation of a control does not allow management or
employees, in the normal course of performing their assigned functions,
to prevent or detect misstatements on a timely basis. A material
weakness is a deficiency, or a combination of deficiencies, in
internal control over financial reporting, such that there is a
reasonable possibility that a material misstatement of a fund's
annual or interim financial statements will not be prevented or
detected on a timely basis.

Our consideration of the Funds' internal control over financial
reporting was for the limited purpose described in the first
paragraph and would not necessarily disclose all deficiencies in
internal control that might be material weaknesses under standards
established by the Public Company Accounting Oversight Board
(United States). However, we noted no deficiencies in the Funds'
internal control over financial reporting and their operations,
including controls for safeguarding securities, that we consider
to be a material weakness, as defined above, as of March 31, 2024.

This report is intended solely for the information and use of
management, the Board of Trustees of MFS Municipal Series Trust
and the Securities and Exchange Commission and is not intended
to be and should not be used by anyone other than
these specified parties.

Deloitte & Touche LLP
Boston, Massachusetts
May 15, 2024