Anamorphic basidiomycetous yeast strains RS090(T) and RS092 were isolated from a soil sample collected on Rishiri Island in the Rishiri, Rebun, Sarobetsu National Park, Hokkaido, Japan. As the sequences of the D1/D2 domains of their large-subunit rRNA genes were identical and those of the internal transcribed spacer regions differed in only four bases, we conclude that they belong to a single species with intraspecific diversity. Phylogenetically, this species was related to Dioszegia buhagiarii and Dioszegia hungarica, in the Tremellales, Tremellomycetes, Basidiomycota, but was clearly distinct from them. Based on the results of sequence analyses and phenotypic characteristics, we conclude that they belong to a novel species in the genus Dioszegia, for which the name Dioszegia rishiriensis sp. nov. is proposed, with the type strain RS090(T) ( = JCM 16282(T) = CBS 11844(T)).