Daphnia curvirostris species complex is a cladoceran group (Crustacea: Cladocera) with maximum diversity in Eastern Palearctic. To date, several representatives of this complex are known from the Russian Far East. Here we describe a new species of the Daphnia sinevi species group from water bodies of Sakhalin Island. Morphology of its parthenogenetic females is similar to that in D. sinevi from the continental part of Asian Eurasia. However, we found diagnostic traits of D. sakhalinensis sp.nov. in morphology of the second pecten on postabdominal claw, armature of seta 2 on exopodite III, proportions of setae 1/ and 2 length on exopodite V, relative length of male rostrum and structure of the second pecten of male postabdominal claw. This work contributes to our full revision of the D. curvirostris species complex. Separation between continental and Sakhalin populations of D. sinevi group probably happened in Pliocene (about 5 MA) when Sakhalin began to separate from the mainland. However, we cannot exclude a version that populations of D. sakhalinensis sp.nov. appeared as a result of colonization of Sakhalin from the continent and further independent evolution of the island populations.