The number 12 bus, which runs between Dulwich Library to Oxford Circus, is to be entirely served by new Routemaster buses, Transport for London has said.
The 24-hours a day route, which includes Peckham Rye and Elephant and Castle, will be running entirely with the buses from the end of April.
The Routemasters, which have three sets of doors and two staircases, were introduced to help cut emissions.