The leech Myxobdella sinanensis （Oka, 1925）, which is endemic to Japan is facultative parasitic against freshwater Japanese crab, Geothelphusa dehaani（White, 1847）. Whereas they inhabit headwater streams in Japan, their interactions and behavioral responses have not been investigated before. Therefore, the purpose of this study was to elucidate the interaction between the above two species, which have a predator-prey relationship, by focusing on the behavior of both species. One male and one female crab was put in a tank in which leeches (n = 4) were kept in an incubator, and recorded their behavior using a video camera. Survival ratio of the crab sucked by the leech was 17 % (N = 35). Whereas no bias was observed on the parasitized ratio between male (N = 17) and female (N = 18), when male crabs were parasitized, most of the leech attached on the left side of the forceps (P < 0.05). The survival crabs were attached longer time by the leech than the dead individuals. Whereas most of the crabs that encountered the leech within 14 days fled when the leech approached them, their memory seems not last long.