Exhibit 5.1

February 19, 1999




Corporate Office Properties Trust
401 City Avenue, Suite 615
Bala Cynwyd, PA  19004

Ladies and Gentlemen:

This opinion is furnished in connection with the registration on Form S-3
initially filed on February 4, 1999 with the Securities and Exchange Commission
(the "Commission") under Registration No. 333-71807 (the "Registration
Statement") pursuant to the Securities Act of 1933, as amended (the "Securities
Act"), and Rule 415 thereunder for the offering by Corporate Office Properties
Trust, a Maryland real estate investment trust (the "Company"), from time to
time of its securities (the "Registered Securities"). The Registered Securities
consist of (i) common shares of beneficial interest of the Company, par value
$.01 per share (the "Common Shares"), (ii) preferred shares of beneficial
interest of the Company, par value $.01 per share (the "Preferred Shares"),
(iii) warrants to purchase Common Shares (the "Common Share Warrants") or (iv)
warrants to purchase Preferred Shares (the "Preferred Share Warrants", and
together with the Common Share Warrants, the "Warrants"). The Registration
Statement provides that the Company may offer and sell any combination of the
Registered Securities in one or more offerings up to a total aggregate initial
offering price of $250,000,000. This opinion is being provided at your request
in connection with the filing of the Registration Statement.

In connection with rendering this opinion, we have examined the Registration
Statement and the prospectus (the "Prospectus") which forms a part thereof; the
Amended and Restated Declaration of Trust and the Bylaws of the Company, each as
amended to date; such records of corporate proceedings of the Company as we
deemed material; and such other certificates, receipts, records and documents as
we considered necessary for the purposes of this opinion. In our examination, we
have assumed the genuineness of all signatures, the legal capacity of natural
persons, the authenticity of all documents submitted to us as certified,
photostatic or



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February 19, 1999
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facsimile copies, the authenticity of the originals of such copies and the
authenticity of telephonic confirmation of public officials and others. As to
facts material to our opinion, we have relied, without independent verification,
upon certificates or telephonic confirmations of public officials and
certificates, documents and statements of the Company or representatives or
officers thereof.

For the purposes of this opinion, we have assumed that:

         (a) The issuance, sale, amount, and terms of the Registered Securities
to be offered from time to time by the Company will be authorized and determined
by proper action of its Board of Trustees (or where permitted, a committee of
the Board of Trustees) of the Company (each, a "Board Action") in accordance
with the Amended and Restated Declaration of Trust and the Bylaws of the Company
and applicable law, in each case so as not to result in a default under or
breach of any agreement or instrument binding upon the Company and so as to
comply with any requirement or restriction imposed by any court or governmental
or regulatory body having jurisdiction over the Company, and that at the time of
issuance and sale of the Registered Securities the Company will be validly
existing and in good standing under the laws of the State of Maryland.

         (b) Prior to the issuance of any Common Shares or Preferred Shares
(including Common Shares that are the subject of any of the Common Share
Warrants or Preferred Shares that are the subject of any of the Preferred Share
Warrants), there will exist, under the Amended and Restated Declaration of Trust
of the Company, the requisite number of authorized but unissued Common Shares or
Preferred Shares (and securities of any class into which any of the Preferred
Shares may be convertible), as the case may be, and that all actions necessary
to the creation of any such Preferred Shares (and securities of any class into
which any Preferred Shares may be convertible), whether by amendment to the
Amended and Restated Declaration of Trust or by classification or
reclassification of existing capital stock and the filing of Articles
Supplementary will have been taken, and the terms thereof will conform to the
description thereof in the Prospectus or in any supplement thereto (the
"Prospectus Supplement").

         (c) Appropriate certificates representing the Common Shares or the
Preferred Shares will be executed and delivered upon issuance and sale of the
Common Shares or the Preferred Shares, as the case may be, and will comply with
the Amended and Restated Declaration of Trust and Bylaws of the Company.



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February 19, 1999
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         (d) Any Warrants will be issued under a valid and legally binding
warrant agreement (a "Warrant Agreement") that conforms to the description
thereof set forth in the Prospectus Supplement, and will comply with the Amended
and Restated Declaration of Trust and Bylaws of the Company and applicable law.

         (e) To the extent that the obligations of the Company under any Warrant
Agreement may be dependent upon such matters, the financial institution to be
identified in such Warrant Agreement as warrant agent (the "Warrant Agent") will
be duly organized, validly existing, and in good standing under the laws of its
jurisdiction of organization; the Warrant Agent will be duly qualified to engage
in the activities contemplated by such Warrant Agreement; such Warrant Agreement
will have been duly authorized, executed, and delivered by the Warrant Agent and
will constitute the legally valid and binding obligation of the Warrant Agent
enforceable against the Warrant Agent in accordance with its terms; the Warrant
Agent will be in compliance, generally, with respect to acting as Warrant Agent
under such Warrant Agreement, with applicable laws and regulations; and the
Warrant Agent will have the requisite organizational and legal power and
authority to perform its obligations under such Warrant Agreement.

         (f) The underwriting agreements for offerings of the Securities (each,
an "Underwriting Agreement", and collectively, the "Underwriting Agreements")
will be valid and legally binding contracts that conform to the description
thereof set forth in the applicable Prospectus Supplement.

Based upon the foregoing examination and assumptions, we are of the opinion
that:

         1. Upon due authorization by Board Action of an issuance of Common
Shares, and upon issuance and delivery of certificates for such Common Shares
against payment therefor in accordance with the terms and provisions of such
Board Action, the Registration Statement (as declared effective under the Act),
the Prospectus or the applicable Prospectus Supplement and, if applicable, an
Underwriting Agreement, or upon issuance and delivery of certificates for Common
Shares pursuant to the exercise of one or more Common Share Warrants or the
conversion of one or more series of the Preferred Shares convertible into the
Common Shares, the Common Shares represented by such certificates will be duly
authorized, validly issued, fully paid, and non-assessable.

         2. When a series of the Preferred Shares (and securities of any class
into which any of the Preferred Shares may be convertible) has been duly
authorized and established in accordance with the applicable Board Action, the
terms of the Amended and Restated



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February 19, 1999
Page 4


Declaration of Trust and Bylaws of the Company, and applicable law, and, upon
issuance and delivery of certificates for shares of such series of the Preferred
Shares against payment therefor in accordance with the terms and provisions of
such Board Action, the Registration Statement (as declared effective under the
Act), the Prospectus or the applicable Prospectus Supplement, and, if
applicable, an Underwriting Agreement, or upon issuance and delivery of
certificates for shares of the Preferred Shares pursuant to the exercise of one
or more Preferred Share Warrants, the shares of the Preferred Shares represented
by such certificates will be duly authorized, validly issued, fully paid, and
non-assessable.

         3. When the Warrants (and securities of any class for which the
Warrants may be exercised) have been duly authorized and established in
accordance with the applicable Board Action, the terms of the Amended and
Restated Declaration of Trust and the Bylaws of the Company and applicable law,
and, upon execution, issuance, and delivery of the Warrants against payment
therefor in accordance with the terms and provisions of such Board Action, the
Warrant Agreement, the Registration Statement (as declared effective under the
Act), the Prospectus or the applicable Prospectus Supplement, and, if
applicable, an Underwriting Agreement, the Warrants will constitute valid and
legally binding obligations of the Company.

The foregoing opinion assumes that all requisite steps have been or will be
taken to comply with the requirements of the Securities Act and applicable
requirements of state securities laws regulating the offer and sale of
securities.

We hereby consent to the filing of this opinion as an exhibit to the
Registration Statement and to the reference to us with respect to this opinion
under the heading "Legal Matters" in the prospectus which is a part of such
Registration Statement. In giving such consent, we do not thereby admit that we
are in the category of persons whose consent is required under Section 7 of the
Securities Act. This opinion is expressed as of the date hereof and we disclaim
any undertaking to advise you of any subsequent changes in the facts stated or
assumed herein or of any subsequent changes in applicable law.

Very truly yours,



/s/ Morgan, Lewis & Bockius LLP