Six fire engines and around 40 firefighters were called to a fire at a flat on Garratt Lane in Tooting.
Part of a bedroom in a four-roomed flat on the first and second floor was damaged by fire.
One lady was treated at the scene, she was taken to hospital by London Ambulance Service crews where sadly she died.
The Brigade was called at 1236 and was under control by 1322. Fire crews from Tooting, Wandsworth, Battersea, Clapham and Norbury fire stations were at the scene.
The cause of the fire is under investigation.