A Non Wave-Overtopping Type Seawall in deepwater which effectively prevents wave-overtopping by its curved part has been studied. By using this seawall, the crown height can be reduced compared to a conventional seawall, and extremely large wave run-ups which suddenly occur due to the irregularity of the waves can be effectively prevented. However, it may sometimes be requested to use this seawall accepting some amount of wave-overtopping in exchange for lower crown height. Thus, in this study, wave-overtopping characteristics of the Non Wave-Overtopping Type Seawall were examined with numerical calculations and experiments, and the followings have been understood: 1) the relation between the height of the crown and the rate of wave-overtopping, 2) the influence of the shape parameters in section on the rate of wave-overtopping.