Exhibit 10.1

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

THIS SEVENTEENTH AMENDMENT (the “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 September 23, 2004, by and among the undersigned parties.

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.                                      The Partnership and the General Partner have entered into a certain Contribution Agreement (the “Contribution Agreement”) dated as of August 26, 2004 with The Rubenstein Company, L.P., a Delaware limited partnership (“TRCLP”).

D.                                     The following assignments and other transactions were effected prior to closing under the Contribution Agreement: (1) pursuant to a certain Assignment, Distribution and Assumption Agreement dated as of September 23, 2004, TRCLP has assigned, transferred and distributed to TRC Associates Limited Partnership, a Delaware limited partnership (“TRCALP”), and TRCALP has assumed and accepted from TRCLP, all of TRCLP’s membership interest as sole member of TRC Pinnacle Towers, L.L.C., a Virginia limited liability company (the “Company”), and TRCALP has thereupon become (and has been admitted as) the sole member and the managing member of the Company in place of TRCLP; and (2) pursuant to a certain Assignment and Assumption Agreement dated as of September 23, 2004, TRCLP has assigned and delegated to TRCALP, and TRCALP has assumed and accepted from TRCLP, all of TRCLP’s rights and obligations in, to and under the Contribution Agreement, and TRCALP has thereupon succeeded to and is deemed to be the “Contributor” under the Contribution Agreement for all purposes thereof.

E.                                       As contemplated by Section 2.1 of the Contribution Agreement, TRCALP intends to transfer all of the issued and outstanding membership interests in the Company (the “Contributed Interests”), to the Partnership in exchange for partnership interests in the Partnership having designations, rights and preferences as set forth herein (the “Series I Preferred Units”).

F.                                       The parties desire to amend the Partnership Agreement to provide for the contribution of the Contributed Interests by TRCALP to the Partnership in exchange for the Series I Preferred Units in accordance with Section 2.2 of the Contribution Agreement.

G.                                      The parties signatory to this Seventeenth Amendment, other than the General Partner, are referred to herein as the “Series I Preferred Unit Recipients”.  Pursuant to the Contribution Agreement, the Series I Preferred Units are to be issued to the Series I Preferred Unit Recipients.

Unless otherwise defined herein, all capitalized terms used in this Amendment shall have the same meanings as set forth in the Partnership Agreement.

NOW THEREFORE, in consideration of the foregoing and of the mutual premises set forth herein, the parties hereto, intending to be legally bound hereby, hereby amend the Partnership Agreement as follows, effective as of the date set forth above:

1.                                        The foregoing recitals to this Amendment are hereby incorporated in and made a part of this Amendment.

2.                                        Upon closing of the transactions contemplated by the Contribution Agreement, TRCALP shall contribute the Contributed Interests to the Partnership.

3.                                        Upon the contribution of the Contributed Interests to the Partnership by TRCALP, and in accordance with Section 2.2 of the Contribution Agreement, the Partnership shall issue 352,000 Series I Preferred Units, which Series I Preferred Units shall constitute Senior Preferred Units, to TRCALP.

4.                                        The Series I Preferred Units shall have the following terms and other characteristics: (1) an issuance value of $25.00 per unit; (2) a liquidation preference of $25.00 per unit plus all accrued and unpaid distributions thereon (the “Liquidation Preference”) (in determining the Liquidation Preference, unpaid distributions shall accrue and be compounded on a quarterly basis); and (3) an annual cumulative preferred return thereon (the “Priority Return Percentage”) as described in this Section 4.

4.1.                               The Priority Return Percentage for the period commencing on the Closing Date (as such term is defined in the Contribution Agreement) and expiring on the day immediately preceding the fifteenth (15th) anniversary of the Closing Date shall be 7.50% per year (i.e., $1.875 per unit per year).

4.2.                               The Priority Return Percentage for the period commencing on the fifteenth (15th) anniversary of the Closing Date and expiring on the day immediately preceding the twentieth (20th) anniversary of the Closing Date shall be the greater of (a) the Adjusted Treasury Yield (as defined below) as of the fifteenth (15th) anniversary of the Closing Date and (b) 10.0% per year; provided, in no event will the Priority Return Percentage for such 5-year period exceed 12.0% per year.

4.3.                               The Priority Return Percentage for the period commencing on the twentieth (20th) annive