Police are looking for a man who smacked a woman on the buttocks on a C train in Brooklyn.

The man approached the 25-year-old victim on the northbound train inside the Ralph Avenue station in Bedford-Stuyvesant around 9:40 a.m. on Sept. 24 and smacked her, the NYPD said.

The suspect then got off the train and ran off.

Police have released surveillance photos of the man, who they say was last seen wearing white sneakers, a white shirt and brown pants.

Anyone with information is asked to call Crime Stoppers at 800-577-TIPS.