The essential oil fraction was obtained from the leaves and flowers of Artemisia iwayomogi (Compositae) by steam distillation, and its main component, vulgarone B, was isolated by column chromatography. RAW 264.7 cells were used to investigate the anti-inflammatory properties of A. iwayomogi and vulgarone B. Cell viability was determined by MTT assay after treatment with various dilutions of the compounds. In addition, several assays were used to determine the effects of A. iwayomogi essential oil components on immune stimulation. Nitric oxide production in cells activated with lipopolysaccharide (LPS) was evaluated by reaction with Griess reagent. Both vulgarone B and the essential oil fraction of A. iwayomogi inhibited the production of nitric oxide. The effects on various cytokines released from the cells were also measured using ELISA. The production of prostaglandin $E_2$ was significantly decreased by treatment with A. iwayomogi oils. LPS-induced IL-$1{eta}$ and IL-6 production were also decreased in a dose-dependent manner, but no significant effect on TNF-${alpha}$ was observed at the concentrations tested. Finally, Western blot analysis revealed that A. iwayomogi oils reduced the levels of COX-2 and iNOS.