AIM: To investigate the inhibitory effect of imrecoxib, a synthetic compound of completely new structure, on cyclooxygenase 1 (COX-1) and 2 (COX-2) and its anti-inflammatory effect in vivo. METHODS: The inhibitory effects of imrecoxib on cyclooxygenase 1 and 2 were studied using whole cell assay with murine peritoneal macrophages induced by calcimycin and LPS. The inhibitory effects of imrecoxib on mRNA level of COX- 1 and COX2 in human macrophage cell line U937 were detected by reverse transcription polymerase chain reaction (RT-PCR)analysis. Effects of imrecoxib on acute and chronic inflammation were evaluated in rat carrageenan induced edema model and rat adjuvant-induced arthritis model, respectively. RESULTS: Imrecoxib was found to inhibit COX-1and COX-2 with IC50 value of 115+28 nmol/L and 18+4 nmol/L, respectively. Imrecoxib was shown to selectively and dose-dependently inhibit COX-2 mRNA level. Imrecoxib effectively inhibited carrageenan-induced acute inflammation at the doses of 5, 10, and 20 mg.kg-1 ig and adjuvant-induced chronic inflammation at the doses of 10and 20 rmg.kg-1.d-1 ig. CONCLUSION: Imrecoxib is a novel and moderately selective COX-2 inhibitor that possesses anti-inflammatory effect by inhibition of COX-2 mRNA expression.