The 21-year-old victim was on a train at the 63rd Street station at about 11:16 p.m. when police said the suspect approached him.
Police said the suspect then pulled out a knife and started attacking the victim.
The man was cut twice on his arm and transported to University of Chicago Medical Center in good condition.
The suspect was arrested a short time later and a knife was recovered. Police said. Area One detectives are investigating.