Objective:To observe the anti-tumor effect of arsenic trioxide (As2O3) on SMMC-7721 cells of patients with liver cancer in vivo and vitro. Methods: Methyl Thiazolyl Tetrazolium (MTT) method, fluorescence microscope, FITC-AnnexinⅤ/PI double-tagging method and colorimetry were used to detect the survival rate, morphological change, apoptosis and Caspase-3 activity change of SMMC-7721 cells in different concentration of As2O3 for 48 h, respectively. As2O3 was injected into the transplanted tumors in nude mice with SMMC-7721 hepatoma cells to observe the growth of tumors. The mice were sacriifced after 12 d, followed by the extirpation and weighing of the tumors. Then Bcl-2, Bax and Caspase-3 expression were detected by immunohistochemistry. Results: As2O3 could obviously inhabit the proliferation of SMMC-7721 cells, with inhibition concentration (IC) being (18.17±2.10) μmol/L. Microscope showed typical morphological change of cell apoptosis and As2O3 treatment group was evidently higher than control group in apoptosis rate of SMMC-772 cells, suggesting that As2O3 could improve SMMC-772 cell activity. Internal injection of As2O3 into transplanted tumors in nude mice with SMMC-7721 hepatocellular lines could remarkably inhabit the growth of tumors with inhabiting rate being 52.37%, and immunohistochemistry also revealed that As2O3 could apparently up-regulate cell apoptosis-related Bax and Caspase-3 expression, and down-regulate Bcl-2 expression. Conclusion: As2O3 can inhabit the growth and in vivo oncogenesis of hepatoma SMMC-7721 cells, and induce SMMC-7721 cell apoptosis.