To protest against abortion based on a parliamentary bill that would make pregnancy termination easier, thousands of people gathered for a rally in Paris.
Organisers, among them rightwing religious groups, anti-gay activists and associations for handicapped children, claimed 40,000 people took part. Police put their number at 16,000.
The demonstration was inspired by changes in Spain, where the conservative government last month, under pressure from the Catholic Church, agreed to draft a bill that would ban abortions except in cases of rape or threat to the mother's health.
France's leftwing-dominated parliament is on Monday to start debating a bill that would permit a woman to obtain an abortion if she does not wish to pursue her pregnancy. Current law requires her to show that having a baby would put her "in a situation of distress".
The bill would also punish those who try to prevent a woman from entering places where she can receive information on abortion.
France records around 220,000 abortions a year and it is estimated around one Frenchwoman in three undergoes the procedure in her lifetime. Since a year ago, abortions are reimbursed under the state health system.