A faunal study on the marine decapods of Gogunsan Islands located in the western part of South Korea was performed during the period from August 3 to August 5 in 2003. As a result of the present study, a total 42 species in 17 families (Macrura: four species in two families, Anomura: nine species in four families, Brachyura: 29 species in 11 families) were identified. Of these, two species of shrimp, Athanas sp. and Alpheus sp., are new to Korea. Including these two species, total 20 species in 10 families are newly known to Gogunsan Islands. Fifty two species in 19 families were previously known to occur in this area. Therefore, a total 72 species in 24 families of decapods are now known to occur in Gogunsan Islands. Of the species collected in the present study, Palaemon (Palaemon) serrifer (Stimpson, 1860) in shrimps, Macrophthalmus japonicus De Haan, 1835 living at mud area and Scopimera globosa De Haan, 1835 at sand beach in crabs, and Hapalogaster dentata (De Haan, 1849) in hermits crab were most dominant.