PURPOSE: To provide an outboard engine cooling device allowing the ununiformity of water temperature distribution in a water jacket after start-up to be moderated effectively in a short time.

CONSTITUTION: An outboard engine cooling system is provided with a water jacket 2 for cooling an outboard engine 100 with drawn-up cooling water, a thermostat 3 equipped at the drain hole 2A part of the water jacket 2 and put in valve opening action at the specified temperature, and a cooling water circulating pipe 4 for connecting the cooling water suction side of the cooling water draw-up pump 1 to the other drain hole side separately provided at the water jacket 2. A connecting part between the cooling water suction side of the cooling water draw-up pump 1 and the cooling water circulating pipe 4 is equipped with a change-over valve 5 for communicating either one of the cooling water circulating pipe 4 and a draw-up pipe 1A with the draw-up pump 1.