Police said the victim was riding the Brown Line and got off at the Quincy station at about 10:40 p.m. The suspect followed him from behind and beat and robbed him in the 200-block of West Adams Street, police said.
The suspect is described as black, between 20-30 years old, 5'10"-6'2", 180-200 pounds.
Anyone with information is asked to contact Area Central detectives at (312) 747-8380.