The plankton of the rice paddy field at near Jeou-Dong in Island Wooleoung-Do has been collected with plankton net (No.6) on August 22 in 1973. The results obtained with the simple environmental factors are as followings. 1) The pH averaged was 6.1, and the water temperature was 22℃ averaged in the fifteen stations of the studying area. 2) Five classes, 7 orders, 13 families, 20 genera, 19 species and 3 uncertain species of the phytoplanktons; and 3 classes, 3 orders, 5 families, 6 genera, 5 species with 3 uncertain species of the zooplanktons were identified.