Classification of the living species of rhinoceros has been somewhat controversial. Traditionally, the two-horned rhinoceros, which includes the African (Diceros and Ceratotherium) and the Asian (Dicerorhinus) forms, has been included in one group separate from the one-horned rhinoceros (Rhinoceros). However, recently some authors have regarded the Asian species as a group separate from the African species, irrespective of the number of horns. Furthermore, others have split the living rhinoceros into three unrelated groups that include the African two-horned species in one group, the Asian two-horned rhinoceros in another group, and the Asian one-horned rhinoceros in a third group. We investigated the systematic relationships of the living rhinoceros using high-resolution restriction site mapping of the ribosomal genes of the mitochondrial DNA, and our results support the traditional subdivision of the living rhinoceros based on the number of horns. Few groups of mammals are more critically endangered than the rhinoceros, and the data obtained in this work should provide information relevant to their conservation.