A faunal study on the marine decapods of Saemangeum located in the western part of South Korea was performed during the period from August 21, 2003 to October 25, 2003. Forty four species in 17 families were identified through the present investigation, which were represented by 15 species of shrimps in seven families, three species of anomurans in two families, and 26 species of crabs in eight families. Three species of the identified species were new to Korea: Alpheus sp. and Athanas sp. in shrimps, and Asthenognathus sp. in crab. Of the species collected in the present study, Ogyrides orientalis (Stimpson, 1860) in shrimp, and Acmaeopleura balssi Shen, 1932 and Tritodynamia horvathi Nobili, 1905 in crabs are rare species in the western coast of South Korea.