"We demand free parliamentary elections, press freedom and the release of all political prisoners," Zviad Dzidziguri, an opposition party leader and lawmaker, told reporters. "Those demands have been set out ... but the authorities have been reluctant to fulfill them."
The rally blocked traffic on Rustaveli Avenue, the site of mass anti-government protests last November which led to early presidential polls in the South Caucasus state in January. No clashes were reported.
The opposition has also demanded a recount of the results of the January 5 polls which returned President Mikheil Saakashvili to office.
Opposition leaders said on Friday a wave of hunger strikes would hit the former Soviet republic if the government failed to meet their demands.
"From next Friday, Georgia will be turned into a land of tents, with protests to continue until our complete victory," said Levan Gachechiladze, an opposition candidate who won about 25% of the presidential vote.
Western monitors said Georgia's elections were generally fair, although they admitted there had been a number of violations.
The U.S.-educated Saakashvili has moved to integrate the country into the European Union and NATO since he came to power in 2004, but has been recently criticized for authoritarianism, corruption and economic failures.
His brutal crackdown on protesters in early November triggered public anger and criticism from Georgia's Western allies.
