Moscow police detained 68 people during anti-kremlin protests that drew hundreds of people on New Year's Eve. The Police said about 50 were detained at a similar protest in St Petersburg.
In Moscow, an opposition group had city permission to hold a rally on one corner of a central square and it took place peacefully, with its leaders dressed as father frost and the snow maiden.
Helmeted riot police detained people gathering elsewhere on the square, including prominent opposition leaders Boris Nemtsov and Ilya Yashin.
Protesters demanded that Prime Minister Vladimir Putin step down and called for the release of Mikhail Khodorkovsky, the oil tycoon whose prison sentence was extended on Friday after a trial seen as punishment for challenging Putin's power.
Mr Nemtsov called Mr Putin a threat to Russia: "He cannot run the country, he suffers from a range of manias and we are the hostages of his complexes. Therefore I think the quicker we get rid of him the better it would be for Russia."
The Police spokesman Viktor Biryukov said Nemtsov was detained when he tried to lead a group of protesters on a march.
On Saturday protests were the latest in a series of actions held on the last day of every month with 31 days. The date is a nod to the 31st Article of the Russian constitution, which guarantees the right of assembly.
"It is the most important of our rights because we cannot influence the government," Lyudmila Alexeyeva, who heads the Moscow helsinki group, told the crowd at the sanctioned rally, which took place inside an enclosure that could only be reached by passing through metal detectors.
"We do not have fair elections. We can only have an influence by going out in the street."
Alexeyeva, who at 83 is one of Russia's most respected rights activists, was dressed in the light blue robe of the Snow Maiden.
She debuted the costume at last year's protest, which was banned, and she was pushed into police buses along with the dozens of others who were detained.