Abstract: The poor stability of the ligustilide (LIG) makes its quantitation in Angelica sinensis (AS) difficult. This study establishes a chemical conversion method for the determination of ligustilide content in AS and proposes a national pharmacopoeia standard. Mechanical agitation and sonication of a powdered AS extract in a methanol/cyprolamine mixture facilitated the stabilization and transformation of ligustilide. Using an external reference HPLC-DAD method, the cyclopropyl-ligustilide (LIGc) content in the mixture could be determined. The content of ligustilide was greater than 1.0% based on 144 AS specimens including 68 obtained from the originally planted areas of Qinghai and Gansu Province; 55 specimens were obtained from Minxian and Weiyuan County medicine markets, and 21 specimens for which the storage period reached or exceeded 1.5 years. According to the Hong Kong Chinese materis medica standards, the content of ligustilide in AS should not be lower than 0.6%. The developed method could also be applied to the quality control of other Chinese medicinal materials (such as Ligusticum chuanxiong) or Chinese patent medicines in which ligustilide is the main component.