Abstract: Composition of C, N, and P of some dominant zooplankters: two species of claido cera, one species of copepoda, four species of rotatoria, and two species of protozoa from Lake Donghu, Wuhan has been investigated during their production peak.In terms of the mean percentage of C, N. and P, protozoa takes on the maximum values. However, the ratios of C/N and C/P of the protozoa are the minimal. The percentage of C of Leptodora kindti approximates to that of the protozoa, and that of Neutrodiaptomus incongruens is nearly equal to that of Daphnia hyalina. In percentage of N, Leptodora kindti and Neutrodiaptomus incongruens are almost the same. The percentages of N and P in rotatoria are next to that of protozoa. According to the data calculated, the dry weight per individual of the dominant zooplankters in Lake Donghu is 2.07—2.46 times of their eanbon content.The contents of the three main elements per individual animal are calculated. Regressions together with their coefficients of determination are given to show the relationship between the dry weight per individual and the carbon content of the individual, mostly for planktonic crustaceans. The possibility for constructing a regression for microscopic animals on the basis of the dry weight-carbon per individual is discussed.