Cyclooxygenase (COX-2) has been recently suggested to play a role in hepatocarcinogenesis. However, the exact pathway by which COX-2 affects the growth of hepatocellular carcinoma (HCC) is not clear. This study investigated the effects of a specific COX-2 inhibitor, NS-398, on the cell proliferation and apoptosis of COX-2-expressing and non-expressing HCC cell lines. In addition, the modulatory effect of NS-398 on apoptosis-regulating gene expression was examined. Semi-quantitative/quantitative reverse transcription-polymerase chain reaction and Western blot showed that Hep3B and HKCI-4 cells expressed COX-2 mRNA and protein, but HepG2 cells did not. NS-398 suppressed cell proliferation and induced apoptosis in the two COX-2-expressing cell lines in a dose-dependent manner, but not in HepG2 cells. Fas ligand mRNA and protein expression were increased by the treatment with NS-398 (10 micro M) in COX-2-expressing cell lines. The expressions of Fas and Bcl-2 family genes (Bax, Bcl-2, Bcl-xL, Bcl-xS) were not affected by NS-398 treatment in all three cell lines. In conclusion, specific COX-2 inhibitor suppresses cell proliferation and induces apoptosis in HCC cell lines that express COX-2. Our finding suggests that COX-2 inhibition may offer a new approach for HCC chemoprevention.