Passengers were evacuated from the train and they had to walk along the tracks.
No one was hurt but there were still delays for commuters.
The train derailed around 8 p.m. Thursday night just west of the Cicero stop of the Forest Park branch of the Blue Line.
Bus shuttles were available for passengers between the Pulaski and Oak Park stops, the CTA said.
Trains are now moving through the area with residual delays.
Emergency crews remained on the scene Thursday night, but the CTA says it expects service to be fully restored by the Friday morning rush.