Lieutenant Ed Campbell said there were no injures in the blaze at Holy Trinity Cathedral, at 1520 Green Street. The cause of the fire was not apparent, he said.
Police spokesman Lieutenant Charles Keohane said earlier that arson investigators were looking into the fire as suspicious.
The onealarm fire at the Orthodox church at Green Street and Van Ness Avenue started at 6:09 a.m. and was reported under control at 7:19 a.m., according to the Fire Department.
The parish of Holy Trinity, which was founded in 1857, is the oldest Russian Orthodox parish in the continental United States, he said.
The present cathedral was built in 1909, he said, after the earlier Church was destroyed in the 1906 earthquake.