Abstract: Summarizing the data of rotifers obtained in 1973—1975 and 1979—1982, and comparing with the results of Wang et al. (1965), the authors analyse the species succession and the change in the abundance for the past two decades at two sampling stations, station I and station Ⅱ, which are representative of the bay region and the pelagic zone, respectively.The number of species decreased markedly from 68 species in 1962—1963 to 44 species in 1982 for station I, and from 56 species to 49 species for station Ⅱ. Therefore, in the 1960s the species number at station I was larger than station Ⅱ, but now the situation has been reversed.In general, the standing crop of rotifers at station I is far much greater than at station II thoughout the year. In the pattern of seasonal fluctuation of abundance, the maximum population in each year is usually recorded in summer and in autumn, while the minimum is found in winter and in spring.From the angle of ecology, the authors discuss the species succession as well as the seasonal change in abundance of rotifers in Lake Donghu and probe into the trend of development of rotifers in the lake.