The unidentified victim was attacked in the metro’s line one, near the station of Bastille, during rush hour Friday morning.
The person is being treated for major burns to the face and hands after being evacuated by the emergency services.
Police say an inquiry is underway and that the perpetrator is at large.
On Wednesday, a man and a woman were burned by an “unknown liquid” on the metro but police said there was no link.
In Sept 2017, two American college students were injured in a hydrochloric acid attack by a woman at a train station Marseille, southern France.