The after body of RORO ship or car ferry is characterized as follows; the frame line under water plane is very fine in order to improve the performance of propulsion, but the frame line upper water plane is very fat so as to take the broader deck area. Therefore the sectional form near the water plane becomes flat, and the angle between the water plane and the transverse section of ship is smaller than the other ship. These ship may suffer from the wave impact pressure on the stern flare. For this reason, the experimental and analytical studies on the stern flare impact pressure were carried out, and following results were obtained. (1) The fairly good agreement was found between the impact pressure coefficients obtained from the experiment in regular waves with those by Wagner's method. The magnitude of the coefficient was about 1020. (2) The maximum impact pressure which was predicted in irregular head waves from 3 to 11 Beaufort wind scale was about 2030 t/m² for actual ship. This magnitude is smaller than the bow flare impact pressure, but the probability of occurrence of impact pressure is large. So it seems to be probable that the noise and fatigue due to transient vibration induced by the impact force becomes a problem.