The threadfin bream genus Nemipterus Swainson, 1839 (Perciformes: Nemipteridae) currently includes 29 valid Indo-West Pacific species, eight of which have been recorded from Japanese waters. During an ichthyofaunal survey of Tanega-shima Island, Osumi Islands (Kagoshima Prefecture), Japan, a single specimen (246.9 mm standard length) of the Japanese Threadfin Bream Nemipterus japonicus (Bloch, 1791) was collected at a depth of 10 m on 13 January 2020. The specimen was characterized by seven anal-fin soft rays, 47 lateral-line scales, 6 + 10 = 16 gill rakers, a moderately deep body (depth 33.9% of standard length), long pectoral fin (posterior tip vertically level with anal-fin origin), posterior tip of depressed pelvic fin reaching between anus and anal-fin origin, upper lobe of caudal fin filamentous, and body pinkish dorsally and silver ventrally, with 1 longitudinal yellow stripes on the lateral surface, and a reddish blotch on the lateral line above the pectoral fin. Although the species is widely distributed in tropical and subtropical Indo-West Pacific waters from the Red Sea and the east coast of Africa to Taiwan and the Malay Archipelago, and bears the specific and Japanese names japonicus and Nihon-itoyori, respectively, it has at no time been recorded from Japanese waters. Therefore, the present specimen of N. japonicus, described here in detail, represents the first reliable record from Japan and northernmost record of the species in the western Pacific Ocean. The specimen collected from Tanega-shima Island was most likely to have been transported from Taiwan or the Philippines by the Kuroshio Current, the species being unlikely to reproduce in Japanese waters.