About 500 people have demonstrated in a central Moscow square to demand the removal of prime minister Vladimir Putin and his "rule of thieves".
The rally took place peacefully, but police detained a separate group of 20 opposition activists nearby. About 60 protesters also were detained in St Petersburg, one of a number of other cities where demonstrations were held.
Prominent opposition leader Boris Nemtsov, who was arrested and jailed for 15 days after a similar demonstration a month ago, kept up his assault on Russia's long-time leader as he addressed the protesters in Moscow's Triumph Square.
He compared Mr Putin to Egyptian President Hosni Mubarek, who is facing mass unrest after 30 years in power.
"Please, someone tell me how our leadership differs from his," Mr Nemtsov shouted to the crowd from the back of a truck. "Russia has to get rid of Putin."
He has accused Mr Putin of allowing corruption to pervade the corridors of power and of building up considerable personal wealth during his 11 years in power, at the expense of ordinary Russians. He also has denounced Mr Putin's reversal of the democratic achievements of the 1990s.
Russia's beleaguered opposition holds demonstrations on the last day of every month with 31 days to call attention to the 31st Article of Russia's Constitution, which guarantees freedom of assembly.
The city authorised Monday's rally, but it also authorised the rally on December 31, during which 68 people were arrested, including Mr Nemtsov. He was held after the rally while walking across the square to his car.
Mr Nemtsov's arrest drew Western condemnation and mobilised his supporters, who held daily pickets outside the jail where he was being held.
Hundreds of police surrounded the square, but they allowed the demonstrators to disperse after the hour-long rally ended with cries of "Down with the rule of thieves".