An aquatic oligochaete species, Ripistes parasita (Schmidt, 1847) collected from Ganghwado Island in Korea, is described and illustrated. Specimens inhabiting on aquatic vegetation at the edge of the streams were collected with a plankton hand net. Morphological features of present specimens such as the number of long hair chaetae per bundle and their length in VI-VIII, and shape and size of ventral chaetae are concordant with those of previous reports on this species. The genus Ripistes contains one species, R. parasite which is distributed over, Europe, North America and eastern part of Asia including China and Japan. This is the first record of R. parasita in Korea. Aquatic Oligochaeta is an important member of the fresh-water environment because of its contribution to substance recycling as well as its huge abundance and diversity (Martin et al., 2008). Therefore, the taxonomic study of this group is essential for ecological research about freshwater ecosystems. Faunistic studies of aquatic oligochaetes, however, are still in the early stages. Yoon et al. (2000) first reported seven spec-ies collected from Woopo Wetland. Recently, Jung (2011) added one naidid species, Nais variabilis to Korean fauna. The genus Ripistes contains one species, Ripistes parasita which is distributed over Europe, North America and eastern part of Asia including China and Japan. In present study, R. parasita is newly added to the Korean fauna of aquatic oligo-chates with diagnosis and illustrations. Specimens inhabiting on aquatic vegetation at the edge of the streams were collected with a plankton hand net (mesh size, 100 ㎛). Then, they were fixed with 5% formalin solu-tion. At the laboratory, samples were sorted out under the stereomicroscope and moved into 70% ethanol solution. Spe-cimens were mounted on slide glasses in lactic acid, and observed in detail under the Optiphot-2 light microscope (Ni-kon, Tokyo, Japan). Specimens were deposited at the Depart-ment of Science Education in Ewha Womans University. Taxonomy of families and subfamilies follows the classifica-tion system of Erséus and Gustavsson (2002), and Erséus et al. (2008). Stylaria parasita Schmidt, 1847: 320. Nais parasita: Grube, 1851: 104. Pterostylarides parasita: Czerniavsky, 1880: 310. Ripiestes parasitica: Beddard, 1895: 293. Ripistes parasita : Michaelsen, 1900: 31. Pterostylarides macrochaeta Bourne, 1891: 349, Pl. 26, fig. 1. Material examined. 27 individuals, Korea: Incheon, Gang-hwa-gun, Gilsang-myeon, Jangheung-ri, 37° 37′10″N, 126° 30′29″E, 25 Sep 2011, Jung J. Diagnosis. Length 2.53 mm, width 0.23 mm, number of seg-ments 19. Eyes present. Prostomium with a proboscis (length 0.22 mm). Dorsal chaetal bundles beginning in VI with long hair and simple pointed needle ( Fig. 1 A). VI-VIII with setal bundle with 12-16 long hairs (length 0.26-1.18 mm). Poste-rior segments after VIII with 2 hair setae and a simple point-ed needle chaeta. Ventral chaetae bifurcated crotchet, absent in IV and V ( Fig. 1 A); 3-5 chaetae per bundle in II-VIII; 1-6 ventral chaetae per bundle in posterior segments. Ventral chaetae of II-III with proximal nodulus and longer upper tooth ( Fig. 1 B). Ventral chaetae of remaining segments with distal nodulus, upper and lower teeth almost same in length ( Fig. 1 C). Ventral chaetae of posterior segments with a pro-ximal bent between nodulus and proximal end. Stomachal dilatation sudden in VII ( Fig. 1 A). Measurement. Body (length 1.76-4.73 mm; width 0.16-0.27 mm). Proboscis (length 0.16-0.24 mm). Number of segments (19-53). Long hair chaetae in VI-VIII (0.26-1.18 mm). Hair chaete in segments after VIII (0.1-0.14 mm). Distribution. Europe, Lake Baikal, North America, China, Japan, and Korea. Remarks. In the East Asia region, this species was first re-ported from Manchuria (now in China) by Yamaguchi (1940). Next, the species was found in several regions of China (Chen, 1959; Liang, 1962, 1964; Wang and Cui, 2007). Ohtaka (1985) reported its presence in Japan. Morphological features, which were important for identification of this species, such as the number of long hair chaetae per bundle and their leng-th in VI-VIII, and shape and size of ventral chaetae, are iden-tical with those of present specimens.