In this experiment, the rear slope stability of a breakwater armoured with single layer cubes is tested. The influence of five parameters on the rear slope stability is investigated; free board, wave steepness, crest width, rear slope angle and placking density. Futhermore, an attemption is made to correlate the measured overtopping front velocity and overtopping volume to the rear slope stability. The damage of the rear slope is determined by means of photo analysis