The on-vehicle optical sensor cleaning system includes a washer pump that feeds a cleaning liquid, an air pump, a nozzle member, and a controller. The air pump includes a discharge valve and discharges air through the discharge valve. The discharge valve opens when air is compressed in the air pump. The nozzle member includes an ejection port that ejects a gas-liquid mixture toward a sensing surface of an on-vehicle optical sensor to remove foreign matter from the sensing surface. The cleaning liquid from the washer pump and the air from the air pump are mixed in the gas-liquid mixture. The controller controls the washer pump and the air pump. The controller is configured so that the gas-liquid mixture is ejected by storing the cleaning liquid in the nozzle member to cover the ejection port and then feeding the air to the nozzle member.