The purpose of the study is not only to identify the aquatic insect fauna but also to study the community structure of the aquatic insects through the mathematical analysis in the streams of Bugcheju in Cheju Island. Also based on this result, water quality is determined. The results are as follows; 1. The aquatic insects in the streams of Bugcheju are composed of total 33 species, 30 genera, 21 families in 7 orders. Among them 24 species, 22 genera, 17 families in 6 orders are collected from the Oedo stream and 20 species, 18 genera, 14 families in 6 orders are collected from the Gwangryong stream. 2. The numbers of species according to order in the stream of Bugcheju are listed as follows; Ephemeroptera : 5 species, 4 genera in 3 families Trichoptera : 7 species, 7 genera in 7 families Coleoptera : 8 species, 7 genera in 3 families Plecoptera : 2 species, 2 genera in 2 families Hemiptera : 6 species, 5 genera in 3 families Diptera : 3 species, 3 genera in 2 families Odonata : 1 species, 1 genera in 1 families 3. The percentages of individual numbers per m^2 according to order in the streams of Bugcheju are as follows: Oedo stream : Ephemeroptera 53.3%. Trichoptera 29.3% Coleoptera 10.1%, Hemiptera 5.1% Other orders 2.2%, Gwangryong stream : Ephemeroptera 23.8%, Trichoptera 20.9% Coleoptera 46.2%, Hemiptera 8.4% Other orders 0.7% 4. Dominant species are different depending upon the area and their distributions are as follows: Oedo stream : Baetis nla, Stenopsyche griseipennis Gwangryong stream : Deronectes sp., Baetis nla 5. The number of common species in the Oedo and Gwangryong stream are 10; Choroterpes trifurcata, Baetis nla, Cloeon dipterum. Polycentropus sp., Goera japonica, Deronectes hostilis, Deronectes sp., Laccobius bedeli, Aquarius paludum, Asclepios coreanus. 6. Among the 33 species collected in the whole sites, only the 14 species are the same as those of the Seoquipo City, the 8 species are the same as those of the Han River and the 9 species are the same as those of the NakdongRiver. 7. The dominance indices of each area are 0.46 to 0.91 and higher at the Gwangryong stream. 8. The species diversity indices show value of 2.32 at the Oedo stream. But the Gwangryong stream is a little lower; the diversity indices is 2.07. 9. The surveyed areas divided by saprobiensystem according to species diversity indices: Oedo and Gwangryong streams are β-mesosaprobic.