Adopting the method of batch culture, the effect of ammonia nitrogen and nitrate nitrogen at different concentrations on the production of chlorophyll-a and microcystin of Microcystis sp.isolated from Yanghe Reservoir was investigated.Results showed that, when Microcystis sp.was cultured with ammonia nitrogen, contents of chlorophyll-a increased with ammonia nitrogen concen-tration in the logarithmic growth phase.However, the high concentration inhibited the growth of algae cells.The productions of MCRR fluctuated with the increase of ammonia nitrogen concentration.There was a remarkable rise of microcystin productions, reaching to 6.345×10^-8 μg/cell, when the concentration of ammonia nitrogen was 10.0 mg/L.This was significantly different with other treatments.When Microcystis sp.was cultured with nitrate nitrogen condition, contents of chlorophyll-a increased undu-lately with the increasing of nitrate nitrogen concentration, and there was no difference among different groups.The productions of microcystin under high concentration increased with the concentration during the logarithmic growth phase.They increased to 1.223×10^-8 μg/cell when the concentration was 5.0 mg/L, and reached the maximum value which was far less than that of the ammonia nitrogen group.There was no significant difference on the growth of algae between the two nitrogen sources.Ammonia ni-trogen was more beneficial to the synthesis of chlorophyll-a in algae cells with nitrogen concentration increasing under lower concen-tration(1.5-5.0 mg/L) during the logarithmic growth phase.The productions of microcystin under ammonia nitrogen condition were far larger than nitrate nitrogen group at the range of 1.0-10.0 mg/L, and there was significant difference among the groups.Overall, ammonia nitrogen was more easily to lead to the secretion of MCRR in algae cells.