A sanitary napkin includes an elongated main body having a liquid absorbent layer for absorbing and retaining liquid and rear flaps projecting laterally in opposite directions from a rear part of the main body. The sanitary napkin is adapted to be worn with the rear flaps kept in an unfolded state on an inner side of an undergarment. Each rear flap included a first sheet with corrugated regions and a longitudinally-extending strip-shaped or linear smooth region defined between adjacent corrugated regions. Each corrugated region has hills and valleys which extend laterally and alternate with each other longitudinally. The smooth region is free of the hills and valleys or has a smaller difference in level between hills and valleys than the corrugated region.