Objective: To investigate effect of down-regulating the expression of astrocyte elevated gene 1 (AEG-1) on cell apoptosis in breast cancer cells. Methods: Through liposome-mediated method, the breast cancer MCF-7 cells were transfected with AEG-1 siRNA (AEG-1 siRNA group) or negative control siRNA (negative control group), and the untreated MCF-7 cells served as blank control group. The transfection effects were observed, and then the apoptosis and the expressions of the apoptosis-associated protein caspase-3 and caspase-9 in each group of cells were determined by flow cytometry and Western blot analysis, respectively. Results: In AEG-1 siRNA group compared with blank control group, the expression of AEG-1 protein was significantly decreased, apoptosis rate was significantly increased, and the expressions of caspase-3 and caspase-9 were significantly up-regulated (all P<0.05). No significant differences were noted in above indexes between negative control group and blank control group (all P>0.05). Conclusion: Down-regulating AEG-1 expression can promote the expressions of caspase-3 and caspase-9, and thereby induce the apoptosis of the breast cancer cells. Thus, AEG-1 may play a role in apoptosis inhibition in breast cancer cells, and the mechanism is probably related to its regulating the expressions of apoptosis-associated proteins.