AIM:To study the effect of arsenic trioxide (As_2O_3) on humanhepatoma cell line 8EL-7402 in vivo.METHODS:Human hepatoma cell line BEL-7402 culturedin vitro was inoculated into nude mice and arsenic trioxide,5-Fu and saline were injected into abdominal cavity of thenude mice respectively.The volumes of tumor and generalconditions of the nude mice and structural changes of theliver and kidney were observed.Morphologic changes werestudied under electron microscope.Expression of AFP wasinvestigated by immunohistochemical method.RESULTS:As_2O_3 could inhibit the growth of tumon The tumorgrowth inhibitory rate in mice treated with 2.5 mg/kg As_2O_3was 53.42% on the tenth day.The tumor growth inhibitoryrate in mice treated with 5 mg/kg As_2O_3 was 79.280/0 on thefifth day and 96.58% on the tenth day respectively.As_2O_3 didnot damage the liver and kidney of nude mice,or affect theblood system.Typical apoptotic morphological changeswere found under electron microscope,and the change ofmitochondria was obvious.The expression rate of AFPdeclined after treatment.CONCLUSION:Arsenic trioxide can induce apoptosis ofhuman hepatoma cells,and inhibit proliferation of tumorwith no obvious side effects on liver and kidney. AIM: To study the effect of arsenic trioxide (As_2O_3) on human hepatoma cell line 8EL-7402 in vivo. METHODS: Human hepatoma cell line BEL-7402 cultured in vitro was inoculated into nude mice and arsenic trioxide, 5-Fu and saline were injected into abdominal cavity of thenude mice respectively. These volumes of tumor and general conditions of the nude mice and structural changes of the liver and kidney were observed. Morphological changes were staged under electron microscope. Expression of AFP was investigated by immunohistochemical method .RESULTS: As_2O_3 could inhibit the growth of tumon The tumorgrowth inhibitory rate in mice treated with 2.5 mg / kg As_2O_3 was 53.42% on the tenth day. The tumor growth inhibitory rate in mice treated with 5 mg / kg As_2O_3 was 79.280 / 0 on thefifth day and 96.58% on the tenth day respectively. As_2O_3 didnot damage the liver and kidney of nude mice, or affect the blood system.Typical apoptotic morphological changes found under electron microscope, and the change of mitocho ndria was obvious. The expression rate of AFP declined after treatment. CONCLUSION: Arsenic trioxide can induce apoptosis of human hepatoma cells, and inhibit proliferation of tumor with no obvious side effects on liver and kidney.