An ecological study of aquatic insects was conducted at Chojong stream from September 1992 to August 1993. The taxa of aquatic insects of the study period composed of 152 species, 94 genera, 53 families, 9 orders. Dominant taxa were Ephemeroptera(53%), Trichoptera(34%) and Diptera(10%). Functional feeding groups dominated scrapers and collectors at upper stream(site 1, 2 and 3), filterers and collectors abundanced at middle stream(site 4, 5, 6 and 7). Tolerance groups dominated at middle stream. Monthly diversity indicies were relatively inconsistant at the sites 4 and 5 compared with other sites. Study sites were clustered most similar sites between 4, 5 and 7 by UPGMA. Chojong stream was characterized by water quality in the phase of β-mesosaprobic and α-mesosaprobic.