A detergent supply system for a kitchen hood has a mounting case perpendicularly attached to the kitchen hood, a detergent dispenser with a pump, a wastewater collector and a detergent reservoir mounted higher than the detergent dispenser is mounted. By mounting the detergent dispenser, wastewater collector and the detergent reservoir inside the mounting case, the detergent supply system can be conveniently attached to a self-cleaning kitchen hood.