INTERNAL CONTROL RPT

Report of Independent Registered Public Accounting
Firm


To the Shareholders and
Board of Trustees of MFS Series Trust I

In planning and performing our audits of the financial
statements of MFS Value Fund, MFS Core Equity Fund,
MFS New Discovery Fund, MFS Research International
Fund, MFS Technology Fund and MFS Low Volatility
Equity Fund (the "Funds") (six of the portfolios
comprising MFS Series Trust I (the "Trust")) as of and
for the year ended August 31, 2018, in accordance with
the standards of the Public Company Accounting
Oversight Board (United States), we considered the
Trust's 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 Trust's internal control over
financial reporting. Accordingly, we express no such
opinion.

The management of the Trust 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 company'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 U.S. generally accepted accounting
principles. A company'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 company; (2) provide
reasonable assurance that transactions are recorded as
necessary to permit preparation of financial statements in
accordance with U.S. generally accepted accounting
principles, and that receipts and expenditures of the
company are being made only in accordance with
authorizations of management and directors of the
company; and (3) provide reasonable assurance
regarding prevention or timely detection of unauthorized
acquisition, use or disposition of a company'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 the company's annual or interim
financial statements will not be prevented or detected on
a timely basis.
Our consideration of the Trust's 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 Trust's
internal control over financial reporting and its
operation, including controls over safeguarding
securities, that we consider to be a material weakness as
defined above as of August 31, 2018.





This report is intended solely for the information and use
of management and the Board of Trustees of MFS Series
Trust I 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/ ERNST & YOUNG, LLP


Boston, Massachusetts
October 16, 2018

INTERNAL CONTROL RPT

REPORT OF INDEPENDENT
REGISTERED PUBLIC ACCOUNTING
FIRM
To the Board of Trustees of MFS Series Trust I
and Shareholders of MFS Low Volatility Global
Equity Fund and MFS U.S. Government Cash
Reserve Fund:
In planning and performing our audits of the
financial statements of MFS Low Volatility
Global Equity Fund and MFS U.S. Government
Cash Reserve Fund (each a series of MFS Series
Trust I) (the "Funds") as of and for the year
ended August 31, 2018, 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 operation, including
controls for safeguarding securities, that we
consider to be a material weakness, as defined
above, as of August 31, 2018.
This report is intended solely for the information
and use of management, the Board of Trustees
of MFS Series Trust I 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 16, 2018