A new species, Rhizothrix sejongi, is described from a sandy beach at Sangju, south coast of Korea. This species bears a superficial resemblance to Rhizothrix gracilis in the fused endopod and exopod of the fifth thoracopod, the four-segmented antennule, and the armature formula of the antennary exopod. The Korean species is unique in its bifid rostrum and short caudal rami, and the armature formula of the endopod of the fifth thoracopod in the female; it is distinguishable from congeners by the broad denticles on the whole body surface. A key to the species of genus Rhizothrix is provided.