Flora and standing crops of the periphyton communities were examined at five sites in the mountainous streams of the Dam of Peace, Korea, from June to November 2003. The attached algal communities comprised totally 76 taxa belong to the 5 classes. In species composition, diatoms and green algae overwhelmingly dominated the periphyton communities although their standing crops were low. During the survey period, major dominant species were Navicula gregaria and Nav. pupla var. capitata, as 11.7% and 8.9% of total standing crop, respectively. Other subdominant species were Scenedesmus ecornis and Spirogyra weberii in green algae, Cymbella affinis, Cymbella minuta. Fragilaria capucina, Melosira varians, Naw. cryptocephala, Nav. exigua var. capitata, Nav. gregaria, Nit. sublineuris in diatom. In the seasonal appearances, S. ecornis and Oscillatoria nigra were occurred in summer, C. affinis and F. capucina in autumn, and N. sublinearis, and species Spirogyra weberii in winter, respectively.