The protester, who was topless and had the words "Free Riot" written on her chest, cut down a wooden crucifix with a chainsaw, RIA Novosti reported. Two other activists helped pull the crucifix down with a rope.
The protesters were part of the Ukrainian feminist group Femen.
"By this act, Femen is calling on all the healthy forces of our society to mercilessly cut out of our brains the rotten religious prejudices which dictatorships rely upon and which prevent the development of democracy and women's freedom," the Segodnya daily quoted the activists as saying.
The incident happened before three Pussy Riot members -- Nadezhda Tolokonnikova, 22, Maria Alyokhina, 24, and Yekaterina Samutsevich, 30 -- were found guilty of hooliganism and sentenced to two years in prison each. The charges against them stemmed from a Feb. 26 performance in Moscow's Cathedral of Christ the Savior.
Officials said the performance incited "religious hatred."