OBJECTIVE To determine butylidenephthalide in Ligusticum Chuanxiong with RP-HPLC. METHOD The sample was extracted with methanol using sonication. The ESTD was used to quantify butylidenephthalide. HPLC separation was carried out in a Hypersil ODS columm (4.6 mm x 150 mm, 5 microm) , eluted at 1 mL x min(-1) with methanol-5% isopropyl alcohol (60: 40) at 25 degrees C. The detection wavelength was 230 nm. RESULT The linear range was 0.07-0.7 microg for butylidenephthalide. The average recovery was 95.3%, and RSD was 2.3% (n =6). CONCLUSION This method was simple and could be used to determine butylidenephthalide with satisfactory accuracy and reproducibility.