Four fire engines and around 25 firefighters tackled a fire at a flat on East Dulwich Road in East Dulwich.
A small part of a second-floor flat in a five-storey house converted into sheltered accommodation was damaged by the fire. Six people left the building before the Brigade arrived. One man was treated on scene after suffering from smoke inhalation.
The Brigade was called at 1555 and the fire was under control at 1615. Fire crews from New Cross, Brixton, Old Kent Road, and Forest Hill fire stations attended the scene.
The cause of the fire is under investigation by the Brigade and Metropolitan Police Service.