The demonstrators, who waved Georgian flags and EU flags, are demanding a new election under international supervision and an investigation into the alleged irregularities in connection with the election.
The opposition leaders promise to boycott parliament's meetings and hold regular protests until their demands are met.
We will not accept illegitimate elections, we will not recognize an illegitimate parliament, says Badri Japaridze, leader of the opposition coalition Lelo, who spoke at the demonstration.
We will not let Georgian Dream declare itself the legitimate representative of the Georgian people, since it has stolen the election, he continues.
Georgia's leading observer groups have jointly pointed to large-scale and sophisticated fraud and stated that as many as 15 percent of the votes may be invalid.
