A system for cleaning windows in tall buildings, comprises a chassis (7) with means for its mounting on a suspended platform. (3) It also includes a rotating conveyor belt (61) mounted on the chassis and brushes (62) mounted on the conveyor belt. Each brush is mounted through extender means (63). Preferably, the conveyor belt includes means for its rotation in a generally horizontal direction. The means for rotating the conveyor belt include a first roller (71) and a second roller (72) mounted on the chassis. The conveyor belt is preferably mounted between the rollers and further includes motor means for rotating one of the rollers.