Abstract: OBJECTIVE To develope a pre-column derivatization HPLC method for the determination of the content of oleanolic acid in Achyranthes bidentata Bl. METHODS The hydroxyl of oleanolic acid molecules was benzoylated by paranitrobenzoyl chloride as derivatizing reagent. The eluent consisted of acetonitrile-0.2% phosphoric acid solution (95∶5), and the detected wavelength was 254 nm. RESULTS The linear regression equation of derivatives of oleanolic acid was Y=85 197X+22 550 (r=0.999 8), the content of derivatives of oleanolic acid showed a good linearity within the concentration range of 2.0-6.0 μg. CONCLUSION The established pre-column derivatization HPLC-UV method can be used for the determination of the content of oleanolic acid. The derivatives is p-nitrobenzoic acid ester-olean, the UV detected wavelength redshifted from 210 nm to 254 nm. The method is accurate, and compared with previous methods, the effect of the determination and the detection sensitivity is greatly improved, which offered a scientific basis for controlling the quality of Achyranthes bidentata Bl.