The robbery happened at 4:13 p.m. on the train as it traveled between the Halsted and Roosevelt stations, police News Affairs Officer Veejay Zala said.
Two armed suspects took various items from multiple riders, Zala said. No one was seriously hurt and no one was in custody.
Authorities learned about the robbery after one of the riders who was robbed alerted CTA personnel at the Roosevelt station, CTA spokeswoman Catherine Hosinski said.
The transit agency held the train at the Harold Washington Library-State/Van Buren station until police arrived, she said. Service was delayed about eight minutes.
Romelia Garcia (pictured, below) told NBC 5 that she was the only one of about 20 passengers in the train car to fight back. She suffered a bruise on her forehead where one of the men hit her with a gun and other assorted bruises but she refused to give up her purse.
Police are reviewing surveillance video in the case, Zala said.
"Its' not the first time I've seen it done, it's not the first time it's happened, and it's not gonna be the last," said CTA passenger Aida Borjas, who has been robbed on the train before.
Anyone with information regarding the suspects is asked to call Area Central Detectives at 312-747-8380.