Four fire engines and 21 firefighters and officers were called to a fire at a residential healthcare unit in Barkham Terrace, Lambeth.
Part of a bedroom on the first floor was damaged by fire. A total of 54 patients and 15 staff left the building before the arrival of the Brigade. There were no reports of any injuries.
The Brigade was called at 2149 and the fire was under control at 2232. Fire crews from Lambeth and Soho fire stations attended the scene.
The cause of the fire is under investigation by the Brigade and the Metropolitan Police Service.