OBJECTIVE：To establish a method for content determination of steroidal saponin in Allium sativum. METHODS： Pre-column derivatization of steroidal saponin was performed by using the derivatization agent of nitro-benzoic acid-chlorine. And HPLC was conducted to determine the content of steroidal saponin. The column was Shimadzu VP-ODS with mobile phase of acetonitrile - water mixed solution（80 ∶20，V/V）at a flow rate of 1.0 ml/min，the detection wavelength was 254 nm，the column temperature was 25 ℃，and the injection volume of 20 μl. RESULTS：The linear rang of sarsasapogenin was 0-1.25 mg/ml（r＝0.999 0）； RSDs of precision，stability and reproducibility tests were lower than 2％；recovery was 93.1％-96.8％（RSD＝1.56％，n＝6）. CONCLUSIONS： The method is simple，stable with good separation，and can be use for the content determination of steroidal saponin in A. sativum.