The fire began around 5:30 p.m. Saturday on Marco-Polo Avenue near Henri-Bourassa Boulevard East.
Close to 100 firefighters were called to the scene.
They managed to prevent the fire from spreading to neighbouring buildings, but they could not save the mattress factory. It is considered a total loss.
No one was inside the factory at the time of the fire, and no one was injured, according to the Montreal fire department.
The cause of the fire is under investigation.