Abstract: ObjectiveTo compare cytotoxic effects of microcystin-L R(MCLR)on human hepatoma cell lines HT17 and Hep G2,and then study the oxidative DNA damages induced by MCLR.MethodsCytotoxicity was measured by MTT assay,and oxidative DNA damages were detected using immunostaining of 8-hydroxydeoxiguanosine(8-OHdG).ResultsSignificant cytotoxic effects in HT17 cells were observed at MCLR concentrations higher than 1μg/ml.Dose-respond relationship was found between MCLR exposure and cell viability.HT17 cells were more sensitive than Hep G2 cells.MCLR even at non-cytotoxic concentration significantly increased the levels of 8-OHdG.ConclusionHT17 cells with the expression of organic anion transporting polypeptides(OATP)1B1 are more sensitive to MCLR.MCLR even at non-cytotoxic dose induces oxidative DNA damages,which may contribute to their genotoxicity during long-term exposure.