Smoke alarms alerted four people to a fire in their bedsit on Melfort Road in Thornton Heath.
They left before the arrival of the Brigade and there were no report of any injuries.
Around half of a first floor of the property was damaged by fire.
The Brigade was called at 1507 and the fire was under control at 1611. Fire crews from Norbury, West Norwood and Croydon fire stations attended the scene.
The cause of the fire is believed to be due to a hot plate being left on.