Cyclooxygenase is a key enzyme in serpentine biosynthesis, which competitively inhibits catharanthine biosynthesis. In this study, three cyclooxygenase inhibitors (aspirin, ibuprofen and naproxen) were added into Catharanthus roseus (L) G. Don cell suspension culture medium to investigate the regulation effect of the enzyme on the biosynthesis of catharanthine and serpentine. It was shown that naproxen at an appropriate concentration was the most effective cyclooxygenase inhibitor. Naproxen concentration at 8.4 mg/L increased catharanthine content in the cells to 41.8 mg/gDW after 7 day cell culture, which was 5.2 times higher than that of the control. The respective increase and decrease of catharanthine and serpentine in C. roseus (L) G. Don cells were related to the suppression of cyclooxygenase activity caused by cyclooxygenase inhibitors. (C) 2010 Elsevier Ltd. All rights reserved.