Flowers of Magnolia denudata has been reported to possess a variety of pharmacological activities. In this study, we investigated the anti-inflammatory effects and mechanism of the water extract of Flowers of Magnolia denudata(MD) in lipopolysacchride (LPS)-mediated inflammatory mediators in murine peritoneal macrophages. MD itself does not have any toxic effects in murine peritoneal macrophages. MD inhibits LPS-induced nitric oxide (NO), tumor necrosis factor $(TNF)-{alpha}$, IL-6 and IL-12 production in murine peritoneal macrophages. Furthermore, we have found that MD inhibited LPS-induced $NF-{kappa}B$ but not c-Jun N-terminal kinase (JNK), p38 and extracellular signal-ragulated kinase (ERK) activation. These results suggested that MD inhibit LPS-induced production of $TNF-{alpha}$, IL-6 and IL-12 via suppression of the $NF-{kappa}B$ activation.