Although anthropogenic disturbance of 20 years duration affects benthic habitats, few studies have examined its effects on the macrobenthic communities of a bay. The aim of this study was to determine the influence of environmental variables on the macrobenthic communities after the construction of the Hwaong dike. Macrobenthos were collected at 22 sites using a Smith McIntyre grab (0.1 m2) in August 2007 and February 2008. Total organic content was very low around the Hwaong dike. Sediment grain size increased from the Hwaong dike to the outer bay. In total, 317 species of macrobenthic fauna were collected and the mean density was 1,155 ind. m 2, both of which were higher than the results of previous studies. The dominant species, Hetermastus filiformis, known to be a potential pollution indicator, was more abundant near the Hwaong dike. Conversely, species sensitive to organic pollution, such as the polychaete Ampharete arctica and the ophiuroid Amphioplus squamata, exhibited higher mean densities in areas distant from the dike. A cluster analysis indicated that the macrobenthic community was divided into two distinct groups: group I near the dike and group II in the outer bay, which were affected by sediment grain size and total organic content. This study suggests that variations in sediment grain size and organic content after dike construction are important factors controlling the macrobenthic community in Asan Bay.