Matt Forte started the rout with one of his two touchdowns, a 13-yard run with 13:05 left in the first quarter. He scored on a 47-yard second-quarter sprint and finished with 132 yards on 20 carries.
Lance Briggs made two of the defense's four interceptions for the Bears (5-5), who stopped their two-game skid.
St. Louis' Trent Green completed 16-of-30 passes for 219 yards with the four interceptions. He came in when starter Marc Bulger sustained a concussion after only five plays.
Four running backs combined for 14 yards on 19 carries, and Josh Brown averted a shutout with a 43-yard second-quarter field goal for the Rams (2-8), who have lost their last five contests.