Suzaki -bay located in Sikoku island and facing to the pacific ocean has been damaged by tsunamis several times historicaly. In recent years, the Nankai earthquake tsunami in 1946 and the Chillian tsunami in 1960 caused great damage there. In order to prevent the tsunami disaster the construction of the new tsunami-breakwaters of 1420m long are in contemplation at present. 　In the present report, the effect of the breakwaters against tsunamis is investigated by hydraulic model tests. The following mainconclusions are drawn. (1) The inundated water depths and areas are reduced considerably by the instalation of the tsunami breakwaters. (2) The tsunami breakwaters decrease the maximum water surface elevation in Suzaki-bay by 20 to 30 %. (3) The first undulation of the tsunami to the seventh one overtopped the sea walls around Suzaki-bay without tsunami-breakwaters, on the other hand, only two undulations of the first and the forth ones overtopped slightly with the breakwaters.