This work concerns with the biotic study of the polychaeta population in the intertidal flat, Inchon, Korea. Magelona japonica was found to be the most abundant species, comprising 54% of total organisms examined. The presence of large numbers of Magelona japonica and Sternaspis scutata, high value of species diversity indices (H(s)), and the absence of the particular pollution indicator species, except a few Prinospio pinnata, suggest that the study area appears not to be polluted during the study period.