The olive weevil, Pimelocerus perforatus（Roelofs）（Coleoptera: Curculionidae）, is a serious pest of olive cultivation in Japan. Although male and female adults of weevils are generally very similar, we established a simple method for discriminating the sex of olive weevil adults based on external morphology. We found that the first through fourth abdominal ventrites of the females were longer than those of the males, while the fifth abdominal ventrite was shorter. Moreover, the length of the lateral margin of the second abdominal ventrite was markedly different between the sexes. As a result, the ratio of the medial length of the fifth abdominal ventrite to the lateral margin length of the second abdominal ventrite was distinct between the sexes in both wild and laboratory-reared populations of P. perforatus, i.e., the ratio was larger than 0.60–0.65 in females but smaller in males. In addition to this characteristic, the structure of the medial part of the first abdominal ventrite differed between the sexes: it was depressed in the middle in males but inflated in the middle in females. Based on these morphological differences, males and females of the olive weevil were successively discriminated from each other.