AIM: To investigate the relation between the expression of cyclooxygenase-2 (COX-2) and liver cancer, to construct the recombinant adenovirus encoding human COX-2antisense RNA, and to explore its effects on liver cancer cell proliferation.METHODS: We studied the expression of COX-2 in 34cases of hepatocellular carcinoma (HCC) and SMMC7402and SMMC7721 by immunohistochemical technique.Recombinant adenovirus Ad-AShcox-2 was constructed and transfected into human HCC cell lines SMMC7402and SMMC7721, and its effects on COX-2 expression, cell apoptosis and cell cycle were analyzed by flow cytometry.Cell proliferation was determined by colony-forming efficiency.RESULTS: We observed COX-2 expression in 82.4% of HCC and SMMC7402 cells, but no COX-2 expression in SMMC7721 cells. In addition, recombinant adenovirus encoding antisense COX-2 fragment Ad-AShcox-2 was obtained with the titer of 1.06× 1012 PFU/mL. Ad-AShcox-2 could reduce the expression of COX-2 and enhance the percentage of cells in G1/G0 phase in SMMC7402 cell line.The difference of apoptotic index between the Ad-AShcox2 group and control group was statistically significant(tcontrol group= 32.62 and tAd-LacZ= 10.93, P＜0.001) in SMMC7402 but not in SMMC7721. Similarly, colony-forming rates of SMMC7402 and SMMC7721 cell lines, after the transfer of Ad-AShcox-2, were (2.7±0.94)% and(33.6±4.24)%, respectively.CONCLUSION: Reduction in the expression of COX-2 can inhibit COX-2 expressing HCC cells.