This study aims to develop the information service system of integrated seakeeping performance for seagoing vessels. It has been successful in developing the intended system which has made possible to provide the following functions and capabilities: ${ullet}$ immediate computation of the dynamic motions of a ship against the present and future weather conditions; ${ullet}$ evaluation of the integrated seakeeping performance of a ship on a real time basis and providing the navigators with the seakeeping informations on the spot enabling them to take the most appropriate countermeasures; and ${ullet}$ supporting the navigators in the selection of a safe sailing route by providing the integrateseakeeping performance.