A total of 209 people were detained in central Moscow by early today, said the OVD-info watchdog that monitors arrests at opposition rallies.
A police spokesman declined to immediately confirm the figure.
Police said 2,500 people rallied in Moscow to protest the verdict against Russia's top opposition leader who was sentenced to five years in a penal colony on embezzlement charges. Activists said up to 10,000 turned out.
Moscow authorities said the opposition did not receive authorisation to hold the rally, with one city official quoted as saying that protesters were "deliberately" confrontational.
Around 2,000 people also held a protest in Russia's second city of Saint Petersburg, according to AFP reporters.