The huge march on Saturday followed a week of violent clashes between troops and pro-referendum protesters in which at least eight people were killed.
Venezuelan opposition leaders said the big turnout gave fresh impetus to their campaign for Chavez to submit to a recall vote.
"We don’t want bullets, we want votes," Educardo Fernandez, an opposition Christian-Democrat politician, said.
Waving national flags and banners reading "down with dictatorship," protesters denounced what they said were killings and human rights abuses committed by troops in recent protests.
"Our civic resistance must continue in every corner of the country," opposition leader Enrique Mendoza said.
The opposition had submitted a petition signed by several million Venezuelans to force a referendum. But the leftist Chavez says the petition is riddled with fraud.
The National Electoral Council has so far only validated 1.8mn signatures, short of the 2.4mn required by law to trigger a vote.