Sarcocysts of various Sarcocystis spp. are highly prevalent in wild sika deer, Cervus nippon yesoensis, in Hokkaido, Japan, and four species have been identified based on morphological and molecular characteristics: S. ovalis, S. pilosa, S. tarandi-like, and S. truncata-like. The definitive hosts of S. ovalis are corvids, but the hosts of the other species have not yet been identified. Aiming to determine the definitive hosts of these species, we collected 65 red fox (Vulpes vulpes schrencki) fecal samples in eastern Hokkaido and examined them for fecal sporocysts using a modified sucrose flotation method. One fecal sample contained typical Sarcocystis sporocysts, which were identified as S. pilosa based on 18S ribosomal RNA and cytochrome c oxidase subunit I gene sequences. This is the first identification of S. pilosa sporocysts in the wild. These findings indicate that red foxes serve as a definitive host of S. pilosa, and that red foxes constitute a source of S. pilosa infection for deer in Hokkaido.