Two fire engines and 10 firefighters and officers were called to a fire in a terrace house in St Agnes Place, Kennington.
A flat on the first floor was damaged by fire.
One man was rescued by firefighters wearing breathing apparatus and was treated for smoke inhalation at the scene by London Ambulance Service before being taken to hospital.
The Brigade was called at 2057 and the fire was under control at 2145. Fire crews from Clapham and Peckham fire stations attended the scene.
The cause of the fire is under investigation