Recent huge amount of CO2 discharge and the diffusion of detrimental substances by the excessive use of petroleum resources have brought the serious problem of an earth scale such as the global warming. It has been the world common subject for every work of the future to take account of the preserving natural environments. There are several solutions for taking place the petroleum energy. One of them is the wind energy. In 1980’s when the petroleum price jumped up with the twice oil crises, the use of wind power was re-examined. Many kind of modern sailing rigs and new concepts of sail-equipped ships were proposed. These researches are summarized in the international symposiums by RINA, and some of them were successful projects among them. Although the purpose of such sail-equipped ship is obviously the use of the above-mentioned wind energy, it is also empirically known as a secondary effect that the rolling of ship can be reduced by the sail. This comes from the air damping force of sail since the inflow angle of the sail changes with the rolling and this change acts on the direction which decreases the rolling. From this fact, the rolling can be more reduced if the angle of a sail is well controlled against the rolling. In this paper, the roll-damping mechanism is solved based upon the aero and hydrodynamics, and then the control technique of sail angle for decreasing the rolling for various wind directions is proposed, where the sail angle: ??S is simply controlled as ??S=k?, but the polarity of control gain: k must be changed with the wind direction and average sail angle. According to this method, the validity and use of this control have been checked by the model experiments. As the results, it is found that the rolling angle can be remarkably decreased when the ship is sailing against the oblique wind and wave.