Objective: To investigate the effects of a small dose of arsenic trioxide (As2O3) combined with 3’-azido-3’-deoxythymidine (AZT) on proliferative inhibition and apoptosis of hepatoma HepG2 cells and their possible mechanism. Methods: The proliferation inhibition rates of HepG2 cells after treatment with different concentrations of As2O3 and AZT alone and their combination were detected by MTT assay. The combined index of As2O3 and AZT was calculated. The apoptotic rates of HepG2 cells after treatment with As2O3 and AZT alone and their combination were detected by flow cytometry (FCM), and the expression levels of caspase-3, Bcl-2 and Bax mRNAs and proteins were analyzed through RT-PCR and Western blotting, respectively. Results: The proliferation inhibition rate of HepG2 cells in combination of As2O3 and AZT group was higher than that in As2O3 and AZT alone groups (both P < 0.05). The value of combined index was less than 1, indicating obvious synergistic effect between As2O3 and AZT. The apoptotic rate of HepG2 cells after treatment with the combination of As2O3 and AZT was higher than those of the control cells (without any treatment) and As2O3 and AZT alone groups (all P < 0.05). The expression levels of caspase-3 and Bax mRNAs and proteins in combination of As2O3 and AZT group were higher than those of the control group (without any treatment) and As2O3 and AZT alone groups (all P < 0.05). The expression levels of Bcl-2 mRNA and protein in combination of As2O3 and AZT group were lower than those of As2O3 and AZT alone groups (both P < 0.05). The ratios of Bax/Bcl-2 mRNA and protein in combination of As2O3 and AZT group were higher than those of the control group (P < 0.05). Conclusion: As2O3 in combination with AZT has a synergistic effect on proliferative inhibition of HepG2 cells. This effect may be associated with induction of apoptosis, up-regulation of caspase-3 and Bax expressions, and down-regulation of Bcl-2 expression. DOI:10.3781/j.issn.1000-7431.2014.08.005