Abstract: Objective 　To explore the inhibitory effect of As2 O3 on liver metastasis f rom human colon cancer in nude mice. Methods 　BALB/ C2nu/ nu nude mice model of liver metastasis f rom colon cancer was established. As2O3was injected into nude mice 10 minutes, 10 days and 20 days af ter the animals inflicted with liver metastasis f rom colon cancer. The weight of the nude mice, the number, size and weight of the hepatic metastatic lesions, the percentage of hepatic replacement by tumour and the survival period were observed. Results 　The number, size, weight of the hepatic metastatic lesions were obviously inhibited by As2O3 in early time and metaphase ; the percentage of hepatic replacement by tumour was decreased and the survival period of tumor2loading nude mice was prolonged compared with the cont rol ( P < 0. 05) . Con2 clusion 　As2O3 can inhibit the live metastasis f rom human colon cancer in nude mice and early t reatment could be more efficient than metaphase and later.