Abstract: Objective To observe the effects of microcystin-LR(MCLR) on methyltransferase activity in mice liver.Methods Eighty mice were randomly divided into 0,5,11 and 21 μg/kg group according to the dose of MCLR.MCLR was administered for 10 and 20 days,respectively.The liver function and DNA methyltransferase activity were determined.Morphological changes of livers were observed.Results Compared with the 0 μg/kg group,the levels of alanine aminotransferase(ALT),aspartate aminotransferase(AST),alkaline phosphatase(ALP) in serum of the 5 μg/kg group were not obviously different after the exposure of 11 days.The levels of ALT,AST,and ALP in 20 μg/kg group were statistically significantly higher than that of 0 μg/kg group(P<0.05) after the exposure of 11 days.The levels of ALT and AST in 5,10,20 μg/kg group were statistically significantly higher than that of 0 μg/kg group(P<0.05) after the exposure of 21 days.The DNA methyltransferase activity in 5,10,and 20 μg/kg group exposed for 11 days were 89 135.7±14 334.7,92 645.8±15 962.3,and 70 481.3±15 621.25 relative fluorescence unit(RFU)/h/mg,respectively,with statistical differences compared with that of 0 μg/kg group(P<0.05).The DNA methyltransferase activity in 5,10,and 21 μg/kg group exposed for 20 days were 59 115.6±9 884.6,83 310.7±15 066.3,and 86 612.5±20 572.8 RFU/h/mg,respectively,with statistical differences compared with that of 0 μg/kg group(P<0.05).ConclusionMCLR could induce the increases of ALT,AST,ALP levels and up-regulation of methyltransferase activity in mice liver.