Analysis of benthic macroinvertebrate community and biological estimation of water quality by the benthic macroinvertebrates were conducted at Olympic Park at its nearby waters in Seoul from December, 2004 to September, 2005. The benthic macrovertebrates were 49 species. Among them, 39 species of aquatic insects were included 11 species in odonata, 9 species in diptera, 7 species in hemiptera, 6 species in coleoptera, 3 species in ephemeroptera, 2 species in trichoptera and 1 species in lepipdoptera, and 10 species of non-insects were 6 species in mollusca, 2 species in hirudinea and 2 species in oligochaeta. Species number of lakes, Seongnae Stream within and outside the Olympic Park was 25 species, 35 species and 33 species, respectively. Individual number of lakes, Seongnae Stream within and outside the Olympic Park was $131;inds/2.5m^2;239;inds/2.5m^2;556;inds/2.5m^2$, respectively. Mean dominance indices of lakes, Seongnae Stream within and outside the Olympic Park was 0.74, 0.61 and 0.72, respectively. According to the saprobic system based on the ESB index(Ecological score of benthic macroinvertebrate community), all survey sites are $eta-mesosaprobic$ waters. To increase of abundance of benthic macroinvertebrates, regular interval monitoring has to be enforced and standard of water quality for the ecological ponds of Olympic Park has to be prepared.