To consider impulsive wave force in design is important for a marine structure. However a impulsive phenomenon is complicated to observe according to various kinds of conditions and to act in very short time. This research aimed at obtaining the fundamental data of reinforced concrete slab by the impulsive wave force through the large-scale waterway test. Strains of the reinforced concrete slab and distribution of impulsive wave pressure are measured to know the phenomenon. An effect of impulsive component is small for strains in RC slabs.