Objective: To investigate the effects of gambogic acid (GA) on the proliferation and apoptosis of Human lung adenocarcinoma A549 cells in vitro, as well as the regulation of steroid receptor coactivator-3 (SRC-3) to explore the relationship between them.Methods: The effect of GA on the growth of A549 cells was studied by MTT assay. Apoptosis was detected through Hoechst 33258 staining. RT-PCR and Western blot technologies were applied to assess the expression of SRC-3, whereas, the localization of SRC-3 was determined by using confocal microscopy method.Results: GA presented striking proliferation inhibition potency on A549 cells in vitro in a time- and dose-dependent manner, with the IC50 value for 24 h was 3.17(0.13 μmol/L. Hoechst 33258 staining showed that GA could induce apoptosis in A549 cells. Over-expression of SRC-3 was found in A549 cells, whereas the mRNA and protein expression levels of SRC-3 were significantly downregulated in A549 cells induced by GA in a dose-dependent manner. The disposition of SRC-3 was situated mainly at the nuclear.Conclusion: GA may exert its strong anti-leukemia effects through the regulation of the expression of SRC-3. It may be a new target for the therapy of lung cancer.