Exhibit 10.1

EIGHTEENTH AMENDMENT
TO
SECOND AMENDED AND RESTATED
LIMITED PARTNERSHIP AGREEMENT
OF
CORPORATE OFFICE PROPERTIES, L.P.

THIS EIGHTEENTH AMENDMENT (this “Amendment”) to the Second Amended and Restated Limited Partnership Agreement of Corporate Office Properties, L.P., a Delaware limited partnership (the “Partnership”) is made and entered into as of April 18, 2005, by the undersigned.

Recitals

A.                                    The Partnership is a limited partnership organized under the Delaware Revised Uniform Limited Partnership Act and governed by that certain Second Amended and Restated Limited Partnership Agreement dated as of December 7, 1999, as amended to the date hereof (as amended, the “Partnership Agreement”).

B.                                      The sole general partner of the Partnership is Corporate Office Properties Trust, a real estate investment trust formed under the laws of the State of Maryland (the “General Partner”).

C.                                      Pursuant to Section 11.1(b)(iii), the General Partner desires to amend the Partnership Agreement to reflect the admission, substitution, termination and/or withdrawal of various limited partners in accordance with the terms of the Partnership Agreement.

NOW THEREFORE, the General Partner, intending to be legally bound, hereby amends the Partnership Agreement as follows, effective as of the date set forth above.

1.                                        Exhibit 1, Schedule of Partners, as attached hereto and by this reference made a part hereof, is hereby substituted fo