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, 2023, 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, 2023.

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.


/s/Deloitte & Touche LLP

Boston, Massachusetts
May 15, 2023