A taxonomic study of Megarthrus Curtis in Korea is presented. The genus is represented in Korea by 10 species including M. coreanus Kim and Cuccodoro sp. nov. Megarthrus corticalis Sharp, M. fennicus Lahtinen, M. incubifer Cuccodoro, M. japonicus Sharp, M. montanus Sawada, M. sawadai Cuccodoro, and M. zerchei Cuccodoro and Löbl are reported from Korea for the first time. A diagnosis of the genus and a key to the Korean species are provided. The new species is diagnosed, described, and illustrated and the other species are diagnosed and illustrated. Species distributions are presented, and the effect of these Korean findings on the level of endemism of the Megarthrus fauna of Japan and Far East Russia is discussed.