Thelazia callipaeda is a spirurid nematode that parasitizes the eyes of mammals, including carnivores, lagomorphs, and humans. Although this parasite has been reported in domestic and wild animals in Japan, its presence in the Japanese marten, Martes melampus melampus (Carnivora: Mustelidae), has not been documented. In this study, we examined the ocular parasites of a wild Japanese marten collected in Tsukuba, Ibaraki Prefecture, Japan, and identified T. callipaeda based on morphological and molecular analyses. This is the first record of T. callipaeda infection in the Japanese marten. Our findings suggest that wild Japanese martens serve as a natural host for T. callipaeda, contributing to its transmission in the sylvatic cycle.