A hybrid anti-rolling system was equipped on board of the oceanographic research vessel “MIRAI” (8, 672GT). The greatest advantage of the system is capable of reducing rolling motion by fifty percent. As it is the first system which was applied to a large vessel, it is necessary to examine operational conditions of the system at sea. Rolling and wave heights data collection was carried out to investigate not only the system performance, but also oceanic conditions corresponding to wave heights and wind velocities. Then, the measurement data were analyzed by statistical method. The system was operated up to Sea State 6 in the North Pacific Ocean. It was proved that the system functioned very well and had high reliability.