Abstract: Dianchi Lake is the largest lake in Yunnan Province of China.It is a plateau lake and has been undergoing the process of eutrophication.Phosphorus is the main limited factor for the growth of algae in Dianchi Lake.Water samples collected from D-i anchi Lake as culture medium for Microcystis aeruginosa1The present study aims to illustrate the effects of two organophosphorus pest icides (methamidophs and phoxime) on the growth of Microcystis aeruginosa in the lake water1Meanwhile, the kinetic mechanism of uptake of phosphorus forms by Microcystis was also studied1The results indicated that addition of organophosphorus pesticides to lake water at concentration of 0.8, 1.6, 3.2 mg/L (methamidophs) and 0.02, 0.06, 0.1 mg/L (phoxime) stimulated the growth of Microcystis.Under certain concentration, methamidophs and phoxime could inhibit the growth of Microcystis in theHGZ medium, but accelerate the growth in the lake water.The growth rate of Microcystis was dependent upon the concentration of intracellular phosphorus, and accumulative consumption of phosphorus by the alga was testified.Each phosphorus form was used by the alga rapidly at initial phase of algal growth and the concentration of phosphorus forms changed very limited in subsequent phase.The total soluble phosphorus (TSP) and soluble reaction phosphorus (SRP) were the preferential phosphorus forms used by Microcystis and as P source, dissolved organic phosphorus (DOP) was also utilized by the alga to accelerate the growth of Microcystis1All above characteristic play an important role in promoting Microcystis bloom.