The essential oil fraction was obtained from the underground parts o of Ligusticum chuanxiong (Umbelliferae) by steam distillation, and its main components, Z-ligustilide and butylidene phthalide, were isolated by column chromatography. Its essential oil fraction and the isolated main components were examined for effects on their anti-inflammatory properties in RAW 264.7 macrophage cells to develop a new natural anti-inflammatory drug. The results showed that the L. chuanxiong essential oil fraction and its main components, Z-ligustilide and butylidene phthalide, inhibited the production of nitric oxide significantly in lipopolysaccharide (LPS)-treated RAW 264.7 cells. LPS-induced interleukin-$1{eta}$ (IL-$1{eta}$), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-$alpha$) production was also decreased in a dose-dependent manner. In addition, western blot analysis revealed that the L. chuanxiong essential oil fraction and also its main components, Z-ligustilide, and butylidene phthalide reduced the expression levels of cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS).