Protesters had gathered in the Russian capital today after authorities disqualified a number of opposition candidates from standing in local elections.
Leading activist Lyubov Sobol was arrested before she could reach the rally, attended by 1,500 people.
Video from the rally shows officers using their batons against demonstrators while making arrests.
Russian officials initially said there had been just 30 arrests and 350 attendees.
Monitoring group OVD-Info, which runs a hotline for reporting detentions, had been keeping a running toll, which rapidly jumped from a few dozen arrests to several hundred.