In this study, the hydraulic model experiments on stability of armor blocks are carried out for sloping breakwater and artificial reef. Especially, the influence of incident wave characteristics and arrangement of armor blocks on stability of coastal structures is discussed. As the result, stability of armor blocks depends on the wave period and arrangement of blocks. And the mechanism of disaster damage on armor blocks is different from coastal structures. That is to say armor blocks are damaged by the uplift pressure due to return flow of swash waves in the sloping breakwater, but by the horizontal wave force from breaking waves on the artificial reef. Additionally, initial damage place and damage process are clarified experimentally.
