Abstract: The species succession of Cladocera during 1980—1988 and the effects of various ecological factors on it were investigated in Lake, Donghu Wuhan, a lake mainly stocked with silver carp (Hypophthalmichthys molitrix) and big-head carp (Aristichthys nobilis), both feeding on plankton. Though the most dorminant population of Cladocera was still Daphnia hyalina in spring and winter (from December to May), the dorminant population of Daphnia carinata ssp. was replaced by the population of Diaphanosoma brachyurum in summer and autumn (from June to November). The number of species decreased markedly from 47 in the 1960's to 26 in the 1980's. The major ecological factors affecting species succession were fish predation and food competition among Cladocera. Fish predation and eutrophication had several effects on the size structure of the Cladocera, resulting in diminution of the size of Cladocera.