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, 2022 and for MFS Municipal Intermediate Fund as of and for the period ended
March 31, 2022, 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, 2022.

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 13, 2022