The maneuverability of a light draft vessel in rough sea is discussed by using a maneuvering motion simulation. The calculation method for the simulation is based on the MMG model and can also consider the effects of wind and waves on the ship motion. KVLCC2 (Normal Ballast Condition) is employed for the studied ship and we analyze the maneuverability of the ship in rough sea by changing ship speed, rudder angle, wind speed, wave height and ratio between waveand ship lengths. As a result, we got some knowledge which can be used for the Navigation of a light draft vessel in heavy wind and wave conditions. In the future, we would like to progress this study and present guideline for the vessel’s navigating safely in rough sea.