Hollande said he would enact his "marriage for everyone" plan within a year of coming to power in May, but vocal opposition from religious leaders, some politicians and parts of rural France has divided the country.
Saturday's protest, called the "March for Everyone," included pro-family and Catholic groups. Several thousand people marched in Paris, carrying signs with slogans such as "One child (equals) one father + one mother."
Their final destination was the Invalides monument, the final resting place of Napeolon Bonaparte, the French leader who invented the country's prized civil code, which is still in force today. It states that marriage is a union between a man and a woman, a point the gay marriage bill seeks to overturn. Another reform would be to replace the entries in a child's registry book from "father" and "mother" to "parent 1" and "parent 2."
Elsewhere, France's largest demonstrations - estimated to be several thousand people strong - took place in Toulouse and France's second city, Lyon.
The marches Saturday had a dress code of blue, white and pink - putting a spin on the French tricolore flag's traditional colors of blue, white and red.
A recent survey found that most French favor gay marriage, while support for adoption by gay couples hovers at around 50 percent.
(Copyright 2012 by The Associated Press. All Rights Reserved.)