No one was hurt in Saturday night's incident in the Havana Tower at the Tropicana Casino and Resort.
But it did trigger a fire alarm and caused severe water damage to the rooms.
The incident did not cause any major disruptions at the casino, and only the guests in one of the damaged rooms needed to be moved to different quarters. City firefighters also responded to help pump out excess water.
A casino spokeswoman told The Press of Atlantic City that the water damage affected the room where the sprinkler went off, three more rooms on that floor and the room directly under where the water started flowing.
Information from: The Press of Atlantic City, http://www.pressofatlanticcity.com