Up to now, 31 species of zooplankton belonging to Copepoda, Cladocera, Ostracoda, Rotatoria and larvae insecta; 23 taxa of macrobenthos belonging to Mollusca, Crustacea and Insecta larvae; and 21 species of fish were recorded in Hoan Kiem lake. The density of zooplankton ranged from 12000 to 620000 inds/m3, the highest density occured in March and September. Macrobenthos are often distributed in waters around the Ngoc Son temple and near shores of the lake. Insect larvae and oligochaets predominated in density of macrobenthos. Molluses dominated in biomass. In species composition of fish, some species are released by local people. During smmer, when air and water temperature, and humidity are high caused anaerobic water environment, consequences a mass of fish should be died. It is necessary to improve water environment of Hoan Kiem lake by sediment dredge to raise water level and develop fish aquaculture