The arrests followed a protest by high-school students in the town that descended into violence.
The local authority chief in the department of Yvelines, Jean-Jacques Brot, told Le Parisien newspaper: "Instructions were given to proceed to make arrests.
The town of Mantes-la-Jolie had seen two days of clashes between pupils, local youths and police.
Police sources told Le Parisien some of the youngsters arrested on Thursday were carrying bars, baseball bats and canisters of pepper spray.
Nevertheless the images shocked France's political class.