REPORT OF INDEPENDENT REGISTERED PUBLIC
ACCOUNTING FIRM
To the Board of Trustees of MFS Series Trust XVI and the
Shareholders of MFS Prudent Investor Fund:

In planning and performing our audit of the financial
statements of MFS Institutional Money Market Portfolio
(a series of MFS Series Trust XIV) (the Fund) as of and for
the year ended August 31, 2021, 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
opinion 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 Fund 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 funds
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 funds 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 funds 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 funds 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 its operation, including controls for safeguarding securities,
that we consider to be a material weakness, as defined above, as of
August 31, 2021.
This report is intended solely for the information and use of management,
the Board of Trustees of MFS Series Trust XIV 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
October 15, 2021