The protest was the latest of several demonstrations held around the country since Californians adopted Proposition 8, which amended the California Constitution to define marriage as between a man and a woman.
The initiative overruled a state Supreme Court ruling in May that briefly gave same-sex couples the right to marry.
The California Highway Patrol estimated that about 5,000 people gathered for the protest on the steps of the state capitol.
Many in the crowd held signs calling for equality and separation of church from state. Several banners targeted the Mormon Church whose members helped defeat the measure.
"If the ban on marriage equality was unconstitutional in May, the ban will also be unconstitutional when the Supreme Court makes its decision in January," said incoming Senate President Pro Tem Darrell Steinberg, D-Sacramento.
California's highest court agreed this week to hear three legal challenges seeking to nullify the state's new ban on same-sex marriage. All three cases claim the ban abridges the civil rights of a vulnerable minority group. They argue that voters alone did not have the authority to enact such a significant constitutional change.
Connecticut, which began same-sex weddings earlier this month, and Massachusetts are the only states that allow gay marriage. Thirty states ban the practice, but California and a handful of others allow civil unions or domestic partnerships.
Many in the crowd carried signs describing marriage as a civil rights issue.
Don Barnett, 48, drove about 45 miles from the Sierra foothills town of Placerville to participate in his third rally since Proposition 8 was approved by voters on Nov. 4. He carried a "Dear Santa" sign that read, "All I want for Christmas are my civil rights back.
"The California constitution says everyone has equal rights," Barnett said. "It's not just about marriage. There are other rights gays don't have like serving in the military and adoption."
Speakers at the rally included comedian Margaret Cho, couples who have sued to overturn gay marriage bans and local church leaders.
On a corner across the street from the capitol, Lou Anne Merriam, 52, held a bright yellow "Celebrate Prop. 8" sign. She was joined by about a dozen others who chanted: What about my vote to support Prop. 8?
"I'm here representing the voice of those who believe the people have spoken," Merriam said. "My husband and I have been married for 23 years and we're concerned that our tradition and culture will be stripped from us by a people who already have rights."
