Abstract: Microcystins are a group of closely related cyclic heptapeptides produced by a variety of common cyanobacteria.These toxins cause hepatocyte damage by inhibiting protein phosphastases 1 and 2A, resulting in hyperphosphorylation of a number of different proteins.Furthermore, high incidence of primary liver cancer in Qidong and Haimen in China has been associated with bloom contaminated drinking water.The mechanisms of MC-induced hepatotoxicity and tumor promotion activity have not been fully elucidated.In this study, Using 18 cell lines as materials, the cytotoxicity induced by different concentrations of microcystin-LR (20 and 50Lg/mL-was studied.The morphological observation showed that five cell lines ( PC-3, J82, 786-O, 5637 and VERO-E6-underwent obviouslymorphological changes after 30h treatment with microcystin-LR ( MCLR-with a dose-dependent manner.The cytoxicity of MCLR was determined by LDH leakage that showed a dose-dependent increase in five cell lines treated with MCLR, of which LDH leakage for 5637 and PC-3 were more serious under the same treatment.The SOD activity for five cell lines tended to increase in 20Lg/mL MCLR treatment but sharply decrease in 50Lg/mL MCLR treatment compared with the control cells; the GSH content decreased totally in different treatment.Based on the analysis of the sensitivity discrepancy for MCLR, 5637 cell lines was chosen for the establishment of a cell model for the study of cytotoxicity induced by microcystin-LR.