President Francois Hollande's plans to change French laws legalizing same-sex marriage and allow gay couples to adopt has riled many people who took to the streets to protest.
According to the police, at least 70,000 took to the streets in Paris, which included Catholic groups and other backers of traditional family rights, reports the BBC.
There were other demonstrations in the cities of Lyon, Toulouse and Marseille.
Despite opposition from more than 1,000 mayors and the Catholic Church, Hollande's socialist government approved a bill on the issue earlier this month, which will be debated by parliament in January.
"A child needs a father and a mother, he needs the paternal and the maternal side and with this bill that might not be possible any more. That's the way it is and we can't go against nature," said one protestor, Marthe Vignault.
The head of the French Council of Catholic Bishops, Cardinal Andre Vingt-Trois, recently described gay marriage as "the ultimate deceit".
At present only married couples - not civil union partners - can adopt in France.
A number of European nations, including Germany, Sweden and the UK, already allow gay adoption.