Many breakwaters were damaged by the Great East Japan Earthquake of March 11, 2011. Many of these were destroyed under tsunami overflow. It should be noted that tsunami, which is higher than the design tsunami height, may occur for the future. Therefore, it may achieve the disaster mitigation that the breakwater with resilient structure against tsunami has to be developed. In this research, the physical experiments are conducted by using the various breakwater cross sections to clarify the failure mechanism under tsunami overflow. Through results of experiments of the breakwater with countermeasures against scouring, the resiliency of the breakwaters is verified. The following is the summary.
　1. The destruction of breakwater can be verified by using the safety of sliding, overturning and bearing capacity. If the overflow scours the rubble mound, the safety should be estimated with the cross section after scouring.
　2. Souring due to the overflow decreases the bearing capacity of the rubble mound and it makes the breakwater easy to fall down.
　3. The experimental results show that the widening work improve safety factor against sliding, overturning and bearing capacity. The scouring protection mat and armor block above the rubble mound of the widening work, which means placing rubble on the back of the caisson, is efficient to delay the initial time to scour.
　4. The caisson gradually falls into the hole made by scouring, when the scouring reaches at the lower part of caisson.
　5. The widening work has the efficiency to delay the initial time to scour the rubble mound. The breakwater with widening works is able to withstand larger tsunami height than the design height. It indicates that the breakwater with widening work is the resiliency structure against the external tsunami force.