Abstract: This paper reports the results of estimations of population dynamics and production of Moina micrura and Diaphanosoma brachyurum in Xuanwu Lake in Nanjing. The ecological factors affecting the population dynamics and production of these two species are analyzed. The instantaneous birth rate(b), the instantaneous growth rate(r) and the instantaneous death rate(d) of the cladocera were calculated. Seasonal variations in egg density, mean broodsize and proportion of gravid adults were recorded. The mean growing-season biomass was 87.51 μg dry weight/l for Moina micrura and 9.58 μg dry weight/l for Diaphanosoma brachyurum. The average growing-season production was 8 292.36 μg dry weight/l for Moina micrura and 480.02 μg dry weight/l for Diaphanosoma brachyurum. The average growing-season P/B ratio was 94.76 for Moina micrura and 50.52 for Diaphanosoma brachyurum.