The urbanization is altering the hydrology, water quality, channel form of waterway and changing the composition of biological communities in the aquatic ecosystem. Recently, towns grew bigger by the drift of large numbers of people and the medium and small leather and dyeing industries around the Pocheon and Youngpyeong streams. The discharges of sewage were increased by them. The UII (urban intensity index) was 85 (st. P-3) and 91 (st. P-6) in the Pocheon stream and about 20 in the Youngpyeong stream. A total 141 taxa of epilithic diatoms which were composed of 2 order, 8 family, 30 genera. Dominant species were Navicula saprophila, N. subminuscula, Nitzschia palea, Gomphonema pseudoaugur in the Pocheon stream and Achnanthes alteragracillima, A. convergens, A. minutissima, N. minima, N. fonticola, N. frustulum and Cymbella minuta var. silesiaca in the Youngpyeong stream. It Showed the different composition of dominant species by the urbanization near two streams. In the relationships between UII and environmental factors such as EC, BOD, COD, TN, TP and DAIpo, UII showed the high relations $(r^2>0.8)$. It was the difference of organic pollution according to urbanization. It therefore, was higher the relative abundance and more the numbers of saprophilous taxa in the Pocheon stream than the Youngpyeong stream. The water quality of two streams by biological indicators(DAIpo) was polysaprobic state(st. P-3, P-4, P-5) in the Pocheon stream and was oligosaprobic (Y-1), mesosaprobic (Y-2, 3) and polysaprobic state (Y-4) in the Youngpyeong stream during the investigation periods.