The male endophallic morphology and mitochondrial cytochrome oxidase subunit I (COI) gene of two parapatric species of the acuticollis species group, Platycerus acuticollis and P. albisomni, were examined at the border between the two species. No morphologically inferred hybrid was found. The endophallic and mitochondrial types of each individual were significantly linked, and the two species inferred by both types were essentially parapatric even at a very local level. We inferred that the reproductive isolation between them is high, although introgressive hybridization occurred rarely. The taxonomical assignment of P. acuticollis and P. albisomni as two distinct species is considered appropriate.