A single specimen belonging to the family Diodontidae was collected from Seo-gwi-po, Jeju Island, Korea in July 2013 and was identified as Diodon hystrix Linnaeus, 1758, a species new to the Korean fish fauna. The species is characterized by 14 dorsal fin rays, 14 anal fin rays, spines on the dorsal and ventral surfaces of the caudal peduncle, and many small black spots on all fins except the anal fin. The most similar species, Diodon holocanthus, is well distinguished from D. hystrix by the absence of black spots on the dorsal and caudal fins, and the lack of a spine on the dorsal surface of the caudal peduncle. Accordingly, we describe herein the morphological traits of D. hystrix and suggest its new Korean name, "Jan-jeom-bak-i-ga-si-bok".