Protostrongylus shiozawai (Nematoda: Strongylida) infection is known to occur in the lungs of wild Japanese serows (Capricornis crispus) and, to date, has been classified only by its morphological characteristics, as well as host specificity. To characterize P. shiozawai genetically, a partial sequence of the second internal transcribed spacer (ITS-2) region was determined and compared with those of related nematodes. Our subsequent classification of P. shiozawai based on phylogenetic analysis was consistent with the current classification. Phylogenetic analysis also showed that P. shiozawai is more closely related to Protostrongylus stilesi than to Protostrongylus rufescens. PCR using genetic markers in the ITS-2 region should provide a useful tool for expanded studies of P. shiozawai and other Protostrongylus species.