Abstract: An ocean environment monitoring system has a sensor inside a sensor chamber provided with a pair of electrodes at the inlet port of the chamber and a pump for introducing seawater inside the chamber. When a voyage is applied to the electrodes, seawater is electrolyzed to produce an antifouling substance. By operating the pump and a power supply unit for the electrodes intermittently, the antifouling substance is supplied to the filter, the interior of the sensor chamber and the sensor. The monitoring system is compact, consumes a reduced amount of electric power, performs measurement substantially without producing errors for a prolonged period of time, and effectively prevents settlement of marine organisms onto the sensor.