The Moscow protest was the largest in Russia's post-Soviet history, signaling that Putin's comeback to the presidential job he held from 2000 to 2008 will not be as easy as had been expected only two weeks ago.
On Thursday, Putin insisted that the vote results reflected the people's will and dismissed the protesters as Western stooges.
Putin's United Russia party won nearly 50 percent of the vote, a 20 percent decrease on the number of seats it held in the previous legislature. The opposition and some observers said the slim majority it retained was due to widespread vote fraud.
The widespread protest following the vote reflected popular anger against Putin's party, dubbed by its critics as a "party of crooks and thieves."
"The crooks and thieves have stolen our victory," Oksana Dmitriyeva, a leading member of the opposition Just Russia party wrote in her blog Friday, alleging that her party's victory in St. Petersburg, Russia's second-largest city, was taken away from it through massive fraud.
Putin, who has consistently marginalized the opposition and tightened election rules during his 12-year rule, promised during the call-in show some moves toward liberalization. He proposed placing web cameras in all the country's more than 90,000 polling stations for the March 4 presidential election that he is contesting.
On Friday, he ordered the country's finance and communications ministers to get to work on the cameras plan.
In televised footage of that meeting, he did not specify how the cameras would be deployed, leaving open the question of how effective they might be against vote fraud.
The opposition has dismissed Putin's camera proposal as an attempt to deflect public anger.