In this paper,the high performance liquid chromatography(HPLC) was used to monitor the spatial and temporal distri-bution of dissolved Microcystin-LR and Microcystin-RR in Lake Taihu,and its relationship with physiochemical factors of the lake were also discussed.The results showed that the concentrations of microcystin(MCs) were not different between surface and bottom water in a day,and the highest concentration of microcystins occurred in winter.Concentrations of the MCs changed much during one year in the sampling sites N5 and N1 which located in Zhushan Bay and the western part of Lake Taihu,respectively.General-ly, the concentration of the MC-LR was higher than MC-RR for the year in average while the opposite results appeared in individual month of August and September.Correlation analysis showed that MC-LR was significantly positive correlated with TN,but did not show correlation with TP.During the period of water bloom of cyanobacteria,levels of the MC-LR were significantly positive corre-lated with TP,TN,UV₂₅₄ ,SS,total organic carbon and biomass of cyanobacteria,whereas MC-RR was not significant correlated with all the environmental factors in the statistical test.