This paper studies the numbers, biomass and carbon production distribution of algal picoplankton at two stations in Donghu Lake (Wuhan). Algal picoplankton numbers were 0. 0575 × 10⁵-9. 80 0 9 × 10⁵ind. /mL. The biomass (chlorophyll) were 0. 38-54. 30ug chi. a/ L which contributed to total chlorophyll biomass in annual investigation from 2. 24%-98. 66%. Chla carbon production rates ranged from 0. 0004× 10³-1, 6056× 10³mgC/(m³·h). The percentage contribution by picoplankton to total carbon production ranged from 1.0%-90. 4%.The light and phosphorus nutrient measurements from the laboratory experiments indicate some cffects on oxygen production of picoplankton. The optimum light intensity of algal picoplankton photosynthesis is suggested at 7000-13000 Lx in Donghu Lake. The specificity of ecological environment and formation of algal picoplankton in Donghu Lake arc also discussed.