Abstract: Objective To study the effect and mechanism of 4-amino-1,8-naphthalimide(4-AN) on the sensitive effect of arsenic trioxide (ATO) in hepatocellular carcinoma cells. Methods Hepatocellular carcinoma HepG2 cells were divided into two groups according to whether they were treated with 4-AN or not. Cell viability was evaluated by MTT assay, population doubling experiment and colony formation assay; genic mechanism was explored by 8-OH-dG assay, single cell gel electrophoresis (comet assay) and micronucleus test. Results At 2-10 μmol/L concentration of ATO, the cell viability and colony formation efficiency of the combination group (4-AN+ATO) were significantly lower than that of the ATO group (\P\P\P\P\P<0.05). Conclusion 4-AN can significantly increase the sensitivity of ATO in treatment with hepatocellular carcinoma cells and prevent DNA damage repair may be a primary mechanism for this effect.