Report of Independent Registered Public Accounting Firm

To the Board of Trustees and Shareholders of Putnam Mortgage
Securities Fund:

In planning and performing our audit of the financial statements
of Putnam Mortgage Securities Fund (the Fund) as of and for the
year ended September 30, 2022, 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 opinion on the financial statements and to comply
with the requirements of Form NCEN, but not for the purpose of
expressing an opinion on the effectiveness of the Funds internal
control over financial reporting.  Accordingly, we do not express
an opinion on the effectiveness of the Funds internal control over
financial reporting.

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 companys 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
companys 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 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 companys 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 companys 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 over financial reporting 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 its operation, including controls over safeguarding
securities, that we consider to be material weaknesses as defined
above as of September 30, 2022.

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This report is intended solely for the information and use of the
Board of Trustees of Putnam Mortgage Securities Fund and the
Securities and Exchange Commission and is not intended to be and
should not be used by anyone other than these specified parties.

PricewaterhouseCoopers LLP
Boston, Massachusetts
November 11, 2022




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