Russian police said they detained more than 1,000 people in central Moscow as protesters demanded opposition candidates be allowed to run for the Moscow city council.
About 30 people were disqualified from the election and at least 50 arrests took place before the protest was scheduled to begin.
Opposition leaders said they were barred for political reasons and all 45 Moscow city council seats, which have a five-year-term, are up for election on September 8.