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 mac- rophages induced by calcimycin and LPS. The inhibitory effects of imrecoxib on mRNA level of COX-1 and COX- 2 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-1 and 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 in- flammation at the doses of 5, 10, and 20 mg·kg-1 ig and adjuvant-induced chronic inflammation at the doses of 10 and 20 mg·kg-1·d-1 ig. CONCLUSION: Imrecoxib is a novel and moderately selective COX-2 inhibitor that pos- sesses anti-inflammatory effect by inhibition of COX-2 mRNA expression. 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 macrophage induced by calcimycin and LPS. The inhibitory effects of imrecoxib on mRNA level of COX-1 and COX-2 in human macrophage cell line U937 were detected by reverse transcription polymerase 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-1 and COX-2 with IC50 value of 115 ± 28 nmol / L and 18 ± 4 nmol / L, respectively. Imrecoxib was shown selectively and dose-dependently inhibit COX-2 mRNA level. Imrecoxib effective inhibited carrageenan-induced acute in- flamma tion at doses of 5, 10, and 20 mg · kg -1 ig and adjuvant-induced chronic inflammation at doses of 10 and 20 mg · kg -1 · d -1 ig. CONCLUSION: Imrecoxib is a novel and moderately selective COX-2 inhibitor that pos-sesses anti-inflammatory effect by inhibition of COX-2 mRNA expression.