A sea water inflow prevention device for a marine engine, includes; an intake valve that is installed at an air inlet of the marine engine to open or close the air inlet; and a valve drive portion that one side thereof is connected with the air inlet that is disposed between the intake valve and the marine engine, the other side thereof is connected with the air intake valve, makes the air intake valve open the air inlet, when a negative pressure inside the air inlet becomes larger than a tension of a spring member provided inside, and makes the air intake valve close the air inlet, when the negative pressure inside the air inlet is less than a tension of the spring member.
