Four fire engines and around 20 fire officers were called to a blaze at a block of flats in Pytchley Road, East Dulwich.
Part of a flat, in the first floor of Melbreak House, was damaged by fire.
One man left the property before the arrival of the Brigade and was treated at the scene for smoke inhalation, before being taken to hospital by London Ambulance Service crews.
The Brigade was called at 11.12am and the fire was under control at 12.29pm
Fire crews from New Cross, Old Kent Road, Peckham and Lambeth fire stations attended the scene.