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 Tennessee Municipal Bond 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 Tennessee Municipal Bond Fund, MFS Virginia
Municipal Bond Fund, MFS West Virginia Municipal Bond
Fund and MFS Municipal Income Fund (each a series of
MFS Municipal Series Trust) (the "Funds") as of and for
the year ended March 31, 2020, in accordance with the
standards of the Public Company Accounting Oversight
Board (United States) (PCAOB), 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
PCAOB. However, we noted no deficiencies in the Funds'
internal control over financial reporting and their
operation, including controls for safeguarding securities,
that we consider to be a material weakness, as defined
above, as of March 31, 2020.
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, 2020