Four fire engines and around 25 firefighters were called to a fire at an office block of three floors on Tunstall Road in Brixton.
A small part of a first floor office was damaged by fire.
The Brigade was called at 0052 and the fire was under control at 0235. Fire crews from Brixton, Clapham, and Peckham fire stations attended the scene.
The cause of the fire is under investigation by the Brigade and the Metropolitan Police Service.