Four species of opisthobranch molluscs collected from Jeju Island were identified as Pleurobranchus peronii Cuvier, 1804, Pleurobranchus weberi (Bergh, 1905), Aplysiopsis nigra (Baba, 1949) and Stiliger aureomarginatus Jensen, 1993. All of the species and genera examined here are new to Korea. Pleurobranchus peronii and P. weberi were easily distinguished to each species by dorsal tubercles and markings. In this report, we provided descriptions and photographs of these species for identification.