Recent studies have documented male traits that cause physical harm to their mates during copulation. However, whether or not males sustain injuries during copulation has not been investigated except in sexually cannibalistic species. We found that males were injured by females during copulation in the polygynous cricket Meloimorpha japonica. More than half of the males sustained injuries to their forewings and/or genitalia during copulation. The probability of injury increased with the duration of copulation. The remating rate of females was high when the copulation duration in the first mating was short. These results suggest that copulation duration will be affected by the compromise between the risk of injury for males and paternity assurance.