Abstract: Objective To investigate the possible role of Bcl-2 and Caspase3 in NS-398 induced apoptosis of liver tumor HepG2 cell line. Methods Cell apoptosis is determined by flowcytometry analysis using PI staining.The expression of Bcl-2 and Caspase3 protein was detected by Western blot. Caspase3 activity was evaluated by active Caspase3 apoptosis kit with flow cytometry. Results Selective COX-2 inhibitor NS-398 can significantly induce apoptosis of HepG2 cells line significantly. Flow cytometry assay revealed the apoptotic rate of HepG2 cells treated with different concentrations of NS-398 (0,100,200,300,400μmol/L) was (10.51±1.04)%,(27.79±2.40)%,(45.72±3.32)%,(60.22±2.03)%(P<0.01) respectively, while the apoptotic peak did not appear in the control group (P<0.01).The expression of Caspase3 protein was up-regulated while Bcl-2 protein was down-regulated,and the percentage of the cells with active Caspase3 was (2.67±0.22)%, (9.53±0.15)%, (21.28±0.43)%, (39.63±0.8)%, (63.40±0.69)% (P<0.01). Conclusion Selective COX-2 inhibitor NS-398 may activate Caspase3 by down-regulating the expression of Bcl-2 protein,which causes apoptosis of HepG2 cells.