Patented is a sanitary napkin comprising an elongated main body with a liquid absorbent layer for absorbing and retaining liquid. The elongated main body is symmetrically located about a longitudinal centerline extending in an elongated direction of the elongated main body. Rear flaps are located in proximity to a rear edge of the sanitary napkin and project laterally in opposite directions from laterally opposing side edges of the liquid absorbent layer. 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 includes a first sheet that is corrugated so that each rear flap has adjacent to corrugated regions. At least one strip-shaped or linear smooth region extends continuously over a substantially entire length of each rear flap between the adjacent corrugated regions and in a direction that is substantially parallel to the longitudinal centerline. Each corrugated region has hills and valleys that extend laterally and alternate with each other in a direction that is substantially parallel to the longitudinal centerline. 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.