Firefighters were called at approximately 1 a.m. to the building in the 1600-block of West Madison. ABC7 is told the fire started in a ninth-floor apartment and injured two people inside.
The blaze was extinguished quickly, and the building did not have to be evacuated.
"The fire was contained to one apartment. It was contents that had burned, a mattress fire within the apartment," said Pat Brennan of the Chicago Fire Department.
Paramedics took two people to Stroger Hospital. One was injured critically, and the other was last listed in serious condition.
There was word on what started the fire.