A breakwater caisson composed of steel plate - concrete hybrid members will exhibit excellent mechanical performances that are characterized by high load-carrying capacity and rigidity. By taking these advantages, it is realized to become lightweight of caisson, which contributes to enlargement of a structure and reduction of ground reaction forces.
　This paper proposes an advanced type of breakwater caisson by using cylindrically curved hybrid shell members. Applying curvature to outer walls of caisson contributes to much higher load carrying capacity particularly at the joint between the outer wall and footing. This technique may further improve the durability and construction cost of a breakwater caisson. The verification of these features was undertaken based on the following sub-studies:
　1) Load-carrying capacity of hybrid cylindrical panel
　2) Structural performance of the new type breakwater
　3) Construction method
　4) Comparison with conventional breakwater through practical designs for model breakwaters
　Hybrid curved-members demonstrated higher ultimate strength and toughness than conventional ones. An execution test on a prototype caisson model confirmed to form curved panels without any difficulties. Furthermore, comparison with conventional breakwater was also made through trial design, which indicated that the newlyproposed breakwater caisson is effective to reduce construction cost.