Motions due to waves become a certain limitation of installation works of caisson for breakwater at ocean-facing ports. In this report, characteristics of motions of a caisson for breakwater during installation are discussed both by result of field observations at port of Kochi and numerical simulations. Numerical simulations of motions of caisson are also carried out for installation examples at several ports where face to the Pacific Ocean in Japan. Then, limit conditions on installation works are presented on motions and wave height.