45 chemical components of the essential oil from Ligusticum brachylobum were identified, the main ones being alpha-pinene (45.46%), beta-pinene (18.01%) and limonene (8.19%), etc. In the essential oil, however, no ligustilide was found that makes an effective component of the essential oils from L. sinense cv. chuanxiong and from L. sinense. This result provides a basis for the quality evaluation of the drug.