The BBC reported the rally in the heart of Paris led to about 100 arrests stemming from confrontations between the protesters and police.
While police pegged the crowds at about 150,000, organizers claimed close to a million people were present to voice their opposition to the gay marriage legislation signed into law by President Francois Hollande last week, the British network said. The law also allows gays to adopt children. France is now the ninth European nation and 14th worldwide to legalize same-sex marriage.
The BBC said some protesters herded donkeys, with one carrying a poster that stated: "I am an ass. I voted Hollande."
Member of Parliament Jacques Myard, a member of the conservative UMP party, told the BBC there is a "huge gap between this government and the citizens" concerning same-sex marriage.
"This is something we cannot accept because of the fate of the children," he said.
"Those people are playing God, because they want to marry, but it won't stop at this stage. Then they will adopt, and then we will have children in families where there is no father or no mother."
Marine Le Pen of the far-right National Front also took part in the rally.