The small-sized water strider genus Rhagadotarsus Breddin is known to be widely distributed in Southeast Asia. In a recent survey, we found Rhagadotarsus kraepelini Breddin from Gyeongsangbuk province. This species is known to non-native species in Japan. We provide descriptions and photographs of the external morphology of R. kraepelini. And a key to genera of Korean Gerridae is also provided to facilitate identification.