Phytoplanktons and environmental conditions in the Geum River near Gongju were investigated at three stations in July, 1979. Fifty eight kinds of hytoplanktons were identified and of these, Cyanophyta and Chlorophyta in this area appeared more in the number of species than that in the Han River. The number of species of Chlorophyta was double or more at station 2 and station 3 which were situated near Gongju than at station 1, upperstream of Gongju and the number of species of phytoplankton was also higher at station 2 and station 3 than at station 1. In physicochemcial conditons, water temperature at all of three stations was lower than air temperature and pH might have no significance among these three stations. All of these three stations were characterized as the slower flowing water type of downstream in diatom river community.