Abstract: Objective To study the mechanisms of inhibitory effects of 1,25-Dihydro xyvitamin D₃ on hepatocellular cell line SMMC-7721.Methods SMMC-7721 cells were incubated in culture media with 10nmol/L、50nmol/L and 100nmol/L 1,25-Dihydrox yviatmin D₃ for 2d,4d,6d respectively.MTT test,T rypan blue exclusion test and DNA gel electrophoresis were used.Results 1,25-Dihydrox yvitamin D₃(10-100nmol/L)could inhibit the proliferation of hepatocellular cell line SMMC-7721 in dose dependent manner.DAN gel electrophoresis showed that the apoptosis of the hepato cellurlar cells could be induced by 1,25-Dihydroxyvitamin D₃(50nmol/L).Conclusion It was concluded that 1,25-Dihydrox yvitamin D₃ can inhibit proliferation of hepatocellular cells,probably by the interference of DAN metabolism and cell apoptosis.