Police said the 52-year-old officer was involved in a traffic dispute at a stoplight in the 1000-block of West 87th Street at about 10:37 p.m. after being bumped by a red Kia Sorrento on a Dan Ryan Expressway ramp.
Three people were in the Sorrento when one of them fired shots at the officer's vehicle, hitting the rear window, police said.
The officer was not injured and did not return fire, police said.
Area Two detectives are investigating and no one is in custody.