Port structures have been designed by the deterministic method, in which the uncertainties such as estimation error of design variables have been considered with only one safety factor. By that kind of method, however, it was difficult to show the degree of safety for the structures explicitly.
　Recently, porbablistic design methods have been introduced : the reliability based design method and the limit state design method. This present report aims at applying the probablistic design methods to the design of breakwaters.
　Safety indices against sliding of breakwaters designed with the present design system have been calculated by the reliability based design methods. Moreover, the design way of breakwaters by using the reliability based designmethods (levels 1 and 2) has been established.