Objectives : Sam-Myo-Whan(SMW) has been known traditional prescription with anti- anthritis activities. We investigated inhibitory effects of SMW on lipopolysaccharide (LPS)-induced nitric oxide(NO), $TNF-{alpha}$ and inducible nitric oxide synthase(iNOS) production from RAW264.7 cells and BV-2 Microglia cells. Methods : SMW, which had been extracted with 70% MeOH, concentrated and freeze-dried was used for this experiment. After BV2 mouse brain macrophages and RAW264.7 mouse peritoneal macrophages were pretreated with increasing concentrations of SMW extract for 30min, and then activated with LPS. To investigate cytotoxicity of SMW extract, cell viability was measured by MTT assay. NO production was measured in each culture supernatant by Griess reaction. mRNA expression of iNOS in two type cells was investigated by RT-PCR. $TNF-{alpha}$ production was measured in each culture supernatant by ELISA. Results : SMW extract significantly inhibited LPS-induced NO and $TNF-{alpha}$ production in BV2 cells and RAW264.7 cells dose-dependently. SMW extract also greatly suppressed mRNA expression of iNOS in both type cells activated with LPS. Conclusion : These data suggests that SMW extract may have an anti-inflammatory effect through the inhibition of iNOS expression.