Model experiments of wave forces acting on the member of caisson wall and stress analysis of damaged and non-damaged walls of prototype breakwaters have been carried out in order to investigate the design method of caisson wall against wave forces.
　Experiments were conducted in the large wave channel of 105m long and 2.5m high. And wave forces on the vertical wall which were obtained on the basis of measurements of stress imposed upon a plate or beams made of acrylic glass are compared with calculated ones by an existing wave force formula.
　On the other hand, stress analysis of damaged and non-damaged caisson walls of prototype breakwaters was made on the basis of elastic theory of plate. The results show that calculated stress of concrete and reinforcing bars results in higher value than the allowable stress for most cases of damage.