Several hypotheses have been advanced to explain the functions of copulatory plugs: to store spermatozoa, reduce postcopulatory leakage of semen, or prevent further matings. These hypotheses were examined in captive masked palm civets (Paguma larvata). The results showed that spermatozoa were absent in histological sections of copulatory plugs, and copulatory plugs were dislodged from the vagina during a female's 2nd copulation (time to dislodgment 10.8 min ± 1.2 SE). Time to dislodgment was significantly reduced if copulations with 2 males occurred in rapid succession (6.3 ± 2.7 min). However, some plugs were retained up to 18–22 h after 2nd copulations. Females sometimes mated with 2 partners during 1 night, and plugs of the males could be distinguished morphologically. These results suggest that the copulatory plug functions primarily to prevent leakage of spermatozoa from the reproductive tract of the female.