Repeated rain drop impact plausibly brings about a definite damage in airplane surface materials while the airplane flies in rain fall. When the materials are fiber reinforced plastics (FRP), the damage is more serious. However, FRP is a very attractive material to the aircraft, because its specific strength, that is the strength per unit density, is very high as compared with the other materials such as aluminum alloys. This paper investigates the damage mechanism of the glass fiber reinforced plastics subject to repeated rain drop impact and the residual strength after the certain number of the impacts. This experimental result shows that the residual strength decreases significantly after delamination takes place in the FRP.