Four fire engines and 25 firefighters were called to a fire at a house on Frant Road in Thornton Heath.
Part of a second floor flat on the first floor of the three storey house, that was converted into flats for sheltered accommodation, was destroyed by fire.
Four people evacuated before the Brigade arrived. One man was taken to hospital by London Ambulance Service suffering from smoke inhalation.
The Brigade's 999 Control officers were called at 0037 and deployed fire crews from Norbury, Croydon and Woodside fire stations. The fire was under control by 0131.
The cause of the fire is under investigation by the Brigade and the Metropolitan Police Service.