"Israel murderer, Hollande partner in crime," shouted demonstrators at a rally in Paris, while others gathered in several cities throughout the country, including Marseille, Lyon and Lille, to voice their support for the Palestinians.
Police said around 11,500 protesters attended the Paris demonstration, while organisers put the figure closer to 20,000. In Marseille, more than 2,000 came out to protest, with a similar number braving the rain in Lyon.
As has been the case on previous Gaza demonstrations, protesters' ire was directed at the French government for its support for Israel.
"We are here to declare our total support for the Palestinian resistance and denounce this shameful government (of French President Francois Hollande) for backing the Israeli line," Omar Alsoumi of the Palestinian Youth Movement told the crowds in Paris.
Amar, 60, who protested in Paris, described France's position on the conflict "catastrophic."
"I'm French and I've never been as disappointed with France as I am at this time," he said.
Saturday's demonstrations come as the death toll in Gaza rose to more than 1,660 after a failed humanitarian truce.
The conflict has stirred up huge passions in France — home to the largest Muslim and Jewish communities in western Europe with around five million Muslims and half a million Jews.
There have been weeks of pro-Palestinian protests in the capital, some marred by clashes, arrests and allegations of anti-Semitism in which synagogues were targeted and Israeli flags burnt.