Partial skeletal remains of Mauremys reevesii, consisting of the right second and third costals of an individual, were discovered from late medieval deposit of an archaeological site in Hiroshima Prefecture, Japan. Because the site was a local port town with relatively frequent commercial exchanges then, the turtle may have possibly been brought there through direct or indirect foreign trade in the 15th Century. Current Japanese populations of M. reevesii have generally been considered as descendants of artificially transported individuals from outside Japan in no earlier than the late Edo period (late 18th Century). However, the present finding suggests that the species was actually introduced to Japan in the late medieval period or even earlier.