Seven geographical variation types of G.sobaegensis in South Korea were reported by Kim and Lee(1977) and Lee and Kim (1980). After extensive reexamination, we considered type 4, one of the variation types collectd from various localities of Kyongsangbuk-do Pongwha-gun, as a new species This new species is named as Gammarus longisaeta and fully described and illustrated. Adding this new species, total 9 species of freshwater Gammarus are Known to Korea.