Chelidonii Herba (CHE, Baek-gul-chae in Korean), which has its original description in Gu-Hwang-Bon-Cho, a classic book of oriental Herbal book, is widely used in the treatment of stomach cancer, jaundice, gasrtic ulcer, edema and stomach pain, in Korea, Japan and China. The present study was conducted to evaluate the effect of CHE on the nitric oxide (NO) production, iNOS and COX-2 expression in lipopolysaccharide - activated Raw 264.7 cells. After the treatment of CHE, NO production was monitored by measuring the nitrite content in culture medium, cell viability was measured by MIT assay. COX-2 and iNOS were determined by lmmunoblot analysis. The production of nitric oxide was significantly inhibited by pretreatment (1h) with CHE (0.1-0.3 mg／ml) on LPS-activated Raw264.7 cells. The expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase 2 (COX-2) protein were up-regulated by LPS, but the increased levels of iNOS and COX-2 were inhibited by pretreatment of CHE (0.1-0.3 mg／ml), respectively. Thus, the present data suggest that CHE may play an important role in adjunctive therapy in Gram-negative bacterial infections.