AIM: To investigate the in vitro effects and mechanism of action of cinobufacini on apoptosis of lens epithelial cells (LEC). METHODS: Rabbit LEC were cultured for 72 hours with cinobufacini at different concentrations(0.0 [control], 0.1, 0.2, 0.3mg/L)．The inhibition ratio of cinobufacini acting on LEC was analyzed by ethyl thiazolyl tetrazolium(MTT); the changes in DNA structure, by electrophoresis, and the apoptosis rate, by flow cytometry. The mRNA expression of apoptosis-related genes bcl-2 and bax was examined using the reverse transcription-polymerase chain reaction (RT-PCR). RESULTS: At concentrations of 0.1mg/L-0.3mg/L, cinobufacini inhibited LEC proliferation. The inhibition ratio increased as the concentration of the drug increased. The typical DNA-ladders on electrophoretic gels were observed for extracts of LEC in the treated groups. The higher the drug concentration (0.1, 0.2, and 0.3mg/L) was, the higher the apoptosis rate (20.47±0.65%, 27.14±0.95%, and 33.49±0.77%, respectively) would be. The apoptosis rates in these groups were significantly different from those of the control group (P<0.01). With the drug concentration increasing, the mRNA expression levels of the pro-apoptotic bax increased, whereas those of the anti-apoptotic bcl-2 decreased. CONCLUSION: Cinobufacini can notably induce apoptosis of LEC by decreasing the ratio of bcl-2 to bax in vitro. With its low toxicity, this medication may be effective in the prevention and treatment of posterior capsule opacification．