Stability performances of composite breakwaters such as deformation against wave actions are investigated considering their probabilistic nature. The mean and 5% exceedance values of the damage rate of concrete blocks of horizontally composite breakwater against design wave are twice and ten times the design value of N0=0.3, respectively. The mean value of cumulative damage during 50-year lifetime is 8 times the design value. The mean and 5% exceedance values of the sliding distance against the design wave are 7cm and lm, respectively when a vertical wall of a composite breakwater is designed so that the mean value of the cumulative sliding distance over 50-year lifetime is 30cm. The performance design methods of the breakwaters against wave actions are introduced based on their stability performances.