About 80 helmeted police officers rushed to the building early on Saturday to dislodge about 150 students who had holed up in a classroom and barricaded the doors with desks and chairs. Police pushed through and the students moved to an inner courtyard under the dome of the university and, after a brief stand-off, left peacefully.
Three students were arrested, French radio reported. Police had acted on a demand from the rector of the Paris Academy which runs universities there.
On Friday, police officers, positioned in the square outside the university, had launched teargas after coming under attack from students throwing fire extinguishers, chairs and books from windows. Interior Minister Nicolas Sarkozy decided to return early from a trip to the French West Indies because of the demonstrations.
The sit-in at the university took place as part of growing national protests against a youth employment plan that will make it easier for firms to fire workers aged younger than 26. The government hopes the flexibility will encourage employers to hire young people, safe in the knowledge that they will be able to get rid of them if necessary.
Critics say it would offer younger workers less job security than older colleagues and undermine France's generous employment protections. "It's about our future, and we are determined not to give up," said Elisa Penisson, a 21-year-old undergraduate at the Sorbonne.
A university administrator, Nicolas Boudot, said the protesters wanted to turn the university into "a battlefield", not only against the jobs measure "but also against all of the social problems" that France is facing.
In Tours, 200km southwest of Paris, several hundred students moved onto tracks at the railway station, stopping trains for three hours on Friday, the SNCF rail operator said. Students picketed entrances at several of the country's more than 80 universities.
The main students' union said 45 colleges were affected, though Education Minister Gilles de Robien dismissed those figures as "lies."