AIM: To investigate the anticancer effect of a traditional Chinese medicine gambogic acid (GA) in human gastric cancer line BGC-823 and further study the mechanism of apoptosis induction of GA.METHODS: Low differential human gastric cancer line BGC-823 were treated with GA at different doses and different times, the inhibitory rates were detected by MTT assay. Apoptosis induced by GA in BGC-823 cells was observed by Annexin-V/PI doubling staining flow cytometry assay. And T/C (%) was chosen to detect the inhibition of GA on human gastric adenocarcinoma BGC-823 nude mice xenografts. Apoptosis on nude mice xenografts was observed by Annexin-V/PI doubling staining flow cytometry assay and DNA fragmentation assay. To further determine the molecular mechanism of apoptosis induced by GA, the changes on the expression of bcl-2 and bax genes were detected by RT-PCR.RESULTS: After incubation with GA, low differential human gastric cancer line BGC-823 was dramatically inhibited in a dose-dependent manner. After these cells were exposedto GA for 24, 48 and 72 h, the IC50 value was 1.02±0.05, 1.41±0.20 and 1.14±0.19 μmol/L, respectively. Apoptosis in BGC-823 cells induced by GA was observed by AnnexinV/PI doubling staining flow cytometry assay. The apoptotic population of BGC-823 cells was about 12.96% and 24.58%, respectively, when cells were incubated with 1.2 μmol/L GA for 48 and 72 h. T/C (%) of human gastric carcinoma adenocarcinoma BGC-823 nude mice xenografts was 44.3, when the nude mice were treated with GA (8 mg/kg). Meanwhile, apoptosis induced by GA was observed in human gastric carcinoma adenocarcinoma BGC-823 nude mice xenografts. The increase of bax gene and the decrease of bc1-2 gene expressions were found by RT-PCR.CONCLUSION: The inhibition of GA on human gastric cancer line BGC-823 was confirmed. This effect connects with the inducing apoptosis in BGC-823 cells and the molecular mechanism might be related to the reduction of expression of apoptosis-regulated gene bcl-2, and the improvement of the expression of apoptosis-regulated gene bax. The result was also confirmed in vivo.