EXHIBIT 5.1
                   [LETTERHEAD OF MORGAN LEWIS & BOCKIUS LLP]

February 4, 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 (the
"Registration Statement") pursuant to the Securities Act of 1933, as amended
(the "Securities Act") of 19,952,397 shares (the "Registered Shares") comprising
common shares of beneficial interest, par value $.01 per share (the "Common
Shares"), of Corporate Office Properties Trust, a Maryland real estate
investment trust (the "Company"). The Registered Shares consist of Common Shares
which may be sold from time to time by certain selling shareholders who
currently own 7,876,876 Registered Shares and who may acquire the remaining
12,075,521 Registered Shares either by tendering certain units of limited
partnership interests ("Units") in Corporate Office Properties, L.P., a Delaware
limited partnership, in exchange for Common Shares or by converting Series A
Convertible Preferred Shares of the Company (the "Preferred Shares") into Common
Shares.

In connection with rendering this opinion, we have examined 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 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 upon certificates or
telephonic confirmations of public officials and certificates, documents,
statements and other information of the Company or representatives or officers
thereof.

Based upon the foregoing, in our opinion the Registered Shares currently owned
by the selling shareholders as described above have been legally issued by the
Company and are fully paid and non-assessable and that the Registered Shares
which may be issued to the selling shareholders in exchange for Units when
approved for issuance as provided in the Registration Statement or which may be
issued to the selling shareholders by converting Preferred Shares into Common
Shares will be legally issued, fully paid and non-assessable when so exchanged
or converted.

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 and that the sum of (a) all Common Shares issued as of the date
hereof, (b) any Common Shares issued between the date hereof and the date on
which the Registered Shares are actually issued upon tender of Units or
conversion of the Preferred Shares and (c) the amount of such Shares issued upon
such exchange or tender will not exceed the total number of Common Shares that
the Company is then authorized to issue.

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.

Very truly yours,



/s/ Morgan, Lewis & Bockius LLP