Protesters complained about a surge in violent crime under Chavez and wore shirts emblazoned with the phrase "I also want to be president".
Many people carried Venezuela's red, yellow and blue flag in the march that stretched from the edge of the city's largest slum to a wealthy business district.
Chavez, wearing a baseball jersey with the word "Yes" emblazoned across his chest during door-to-door campaigning in a poor Caracas neighbourhood, said: "If we did a march, we would have 100 times the people they brought today."
Opinion polls give a slight lead to Chavez before a February 15 vote on whether to allow him and other politicians to run for re-election as many times as they like in South America's top oil exporter.
Voters rejected a similar proposal in 2007.
If he loses, Chavez would leave office in four years, but he has not ruled out staging another attempt to change the electoral law.
Another referendum defeat for him could embolden opponents and increase resistance to unpopular spending cuts or a currency devaluation that analysts say might result if oil income remains low.
|Chavez says he still needs more time to build a "21st century socialism" [Reuters]
But Chavez denies he will prohibit private property and has pointed out the government continues to work with foreign oil companies.
A close friend of Fidel Castro, Cuba's former leader, Chavez is a vocal critic of the United States and provides Cuba with cheap oil in return for doctors and advisers.
He has nationalised industries and raised spending on health and welfare since he took office in 1999, but says he needs more time to build what he calls "21st century socialism" in one of the principal oil suppliers to the United States.
Still popular with about half of the population, he has amassed considerable power and most institutions are run by his allies.
Opponents say Chavez is authoritarian and will turn people's homes and possessions over to the state.
He has won multiple elections in the past decade and survived a brief coup, a months-long shutdown of the vital oil industry and a recall referendum.
The opposition only recently made gains against Chavez, defeating the 2007 referendum and winning seats in state and city elections last year.