Objective:To examine the role of p38 mitogen-activated protein kinase (MAPK) in NO production and Inos expression in human endothelial cells stimulated by lipopolysaccharide (LPS). Methods: The NO level in the supatant of the cell culture media was measured with Griess method, expressions of Inos protein and a in vitro cultured endothelial cell line ECV304 were detected with immunofluorescence analysis and reverse transcriptase-PCR respectively. Immunokinase assay was employed to measure P38mapk activity. Results: Compared with the basal level of Inos expression and NO production, the NO level and the expressions of Inos a and protein in the cells were increased after LPS stimulation. P38mapk activity in ECV304 cells exhibited a marked increase at 15 min after LPS stimulation, lasting for about 45 min before gradually decline. The Inos protein and a expressions induced by LPS stimulation was significantly inhibited by SB203580 [4-(4-fluorophenyl)-2-(4- methylsulfinylphenyl)-5-(4-pyridyl) imidazole], a highly specific inhibitor of p38 MAPK. Conclusion: p38 MAPK plays an important role in iNOS expression and NO production in ECV304 cells, and the inhibition of the signal transduction pathway can be effective to reduce the production of iNOS and other cytokines, and therefore constitutes a useful strategy for treating septic shock or inflammation.