A marine propulsion system includes a marine propulsion device, a battery, and a controller. The marine propulsion device includes a propeller shaft, an engine, and an electric motor. The marine propulsion device transmits mechanical power from at least one of the engine and the electric motor to the propeller shaft. The battery supplies electric power to the electric motor. The controller controls the marine propulsion device such that the marine propulsion device is switchable among drive modes including a first drive mode and a second drive mode. In the first drive mode, mechanical power is transmitted from only the engine to the propeller shaft. In the second drive mode, mechanical power is transmitted from only the electric motor to the propeller shaft when the engine is in an idling state.