The net loss for the three months ended Dec. 31 compared with a profit of $16.7 million in the fourth quarter of 2010.
"The on-going difficult operating environment, caused by the weak economic recovery and uncertainty surrounding federal budget cuts made 2011 a challenging year for COPT," Randall M. Griffin, chief executive officer, said in a statement.
Total revenue declined to $139 million from $144.2 million in the fourth quarter of 2010, the real estate investment trust said.
The company reported a $17.9 million loss in funds from operations, which is considered the best measure of a REIT's performance. In the year-earlier period, COPT reported a gain of $52.2 million in funds from operations.
On a per-share basis, diluted funds from operations were 56 cents per share when adjusted for items such as acquisition costs and losses on early extinguishment of debt, a 20 percent drop from 70 cents per share in the fourth quarter of 2010.
As of Dec. 31, COPT — a landlord for government and defense-related tenants — had a portfolio of 238 office properties with 20.5 million square feet and an occupancy rate of 86.2 percent. COPT's rental rates averaged $26.59 per square foot.