Up to 10,000 people gathered in a central Moscow avenue to demand Vladimir Putin's resignation and protest electoral fraud.
The rally had been widely seen as a test of whether the opposition is able to maintain its strength after Prime Minister Putin won a return to the Kremlin.
The turnout was in stark contrast to winter election protests which attracted up to 100,000 people in the largest discontent in Russia's post-Soviet history.
Mr Putin, Russia's president in 2000-2008, had to step down in 2008 to avoid the terms' limitations. He won 64% of the vote last weekend and is set to stay in the Kremlin for the next six years.
"This was not an election. This was a special operation from a thug who wanted to return to the Kremlin," opposition leader and former chess grandmaster Garry Kasparov said from the stage.
Although violations at the presidential vote were numerous, observers, however, have viewed the vote as fairer than December's vote.
But the protesters do not recognize the vote's results.
