To prepare reference substance for quality control of Inula Britannica L., 1-O-acetylbritannilactone was extracted and separated from chloroform extraction of Inula Britannica L. Chemical structure of the 1-O-acetylbritannilactone product was elucidated by ultraviolet spectrometry (UV), infrared spectroscopy (IR), nuclear magnetic resonance (NMR) and mass spectrometry (MS), and the results were in agreement with the reference. The purity of the 1-O-acetylbritannilactone product was 99.5%, which satisfies the need of reference substances of traditional Chinese medicines. A method of high performance liquid chromatography-evaporative light scattering detection (HPLC-ELSD) is described for the determination of 1-O-acetylbritannilactone in Inula Britannica L. The chromatographic conditions include Hypersil ODS-2 column, a mixture of methanol-water (52: 48, v/v) with the flow rate of 1.0 mL/min used as mobile phase. The temperature of drift tube of the ELSD was 90 degrees C. Flow rate of carrier gas was 2.5 L/min. Linear range of 1-O-acetylbritannilactone was 1.37 - 8.21 microLg (r = 0.999 8). The average recovery of 1-O-acetylbritannilactone was 100.2% with the relative standard deviation (RSD) of 1.3% (n = 6). The method is simple, accurate, time saving and reproducible.