A recently discovered, incomplete dentary with preserved incisor, premolar and first molar of a minute castorid from the Dota locality, Kani Basin, early Miocene (ca. 18.5 Ma) Nakamura Formation of the Mizunami Group in central Japan, is described as a new species of the trogontheriine beaver Euroxenomys. It represents the first record of Euroxenomys in Asia and one of the oldest records of this genus. Euroxenomys nanus sp. nov. is smaller than the type species, E. minutus from the Miocene of Europe and more hypsodont, but similar in size to E. inconnexus from the Barstovian of Montana. Dota is the first Asian locality with three cooccurring castorids, Youngofiber sinensis, Minocastor godai, and E. nanus.