Reeves' pond turtle, Mauremys reevesii, is an aquatic geoemydid species that is broadly distributed in East Asia. Like many other Asian turtles, this species is facing an extinction crisis in most countries where it occurs. In Japan, however, this turtle commonly occurs in various freshwater habitats. Although the Japanese populations have generally been considered to be native, a few recent studies have yielded circumstantial evidence that suggested that they had originated from relatively recent artificial introductions from abroad. To evaluate the validity of such a view, we analyzed sequence variations of the mitochondrial cytochrome b gene and the control region in M. reevesii samples from various localities in Japan and adjacent countries. The results revealed the presence of 3 distinct genetic groups (groups A, B, and C) in the Japanese samples, of which groups A and B included haplotypes that were almost identical with some haplotypes from the Korean sample and the Chinese and Taiwanese samples, respectively. Sequences from M. reevesii shell products commercially traded in Taiwan included one that was almost identical to the group C sequence. The current Japanese populations of M. reevesii seem to have been derived from multiple artificial introductions from adjacent countries. This finding implies a need to be concerned about the effect of M. reevesii on the Japanese native wildlife, particularly on the Japanese endemic pond turtle, Mauremys japonica, with which M. reevesii is phylogenetically closely related and reportedly frequently hybridizes in the wild. However, the Japanese population may be useful as a genetically variable stock for conservation of this species, which is highly endangered in most of its range outside Japan.