Abstract: Objective: The purpose of this study was to establish a method for the isolation and purification of ellagic acid from Rosa roxburghii Tratt and to investigate the optimal acidification process condition for extraction of ellagic acid from Rosa roxburghii Tratt. Methods: Rosa roxburghii Tratt dried fruit was used as material, ellagic acid was obtained by acid hydrolyzed, and it was purified by methanol recrystallization. Its purity was determined by high performance liquid chromatography (HPLC), the structure of ellagic acid sample was confirmed by Nuclear magnetic resonance spectroscopy (NMR), infrared spectroscopy (IR), mass spectrometry (MS), high performance liquid chromatography (HPLC), ultraviolet spectroscopy (UV). In addition, with ellagic acid extraction yield as an indicator, acid concentration, extraction temperature, extraction time and liquid ratio as independent variables, based on the single-factor tests, a Box-Benhnken central composite and response surface methodology was designed to explore the optimum extraction conditions. Results: The ellagic acid extract was obtained from Rosa roxburghii Tratt, and its purification was 92% analyzed by HPLC, the maximum absorption wavelength of ellagic acid extract was 254 nm, the molecular ion peak m/z was 301.00, and the infrared absorption wavenumber was consistent with the standard, and its structure was determined by ¹H-NMR and ¹³C-NMR, and the optimal extraction parameters of ellagic acid was obtained by response surface method: Acid concentration 5%, extraction temperature 127 ℃, liquid ratio 8:1 mL/g, extraction time 9.8 h. Under this condition, the highest yield of ellagic acid could reach 30.2%±2.3% (compared to predicted value P>0.05). Conclusion: In this study, a simple and efficient purification method of ellagic acid from Rosa roxburghii Tratt was established and its structure was confirmed, and the optimal process for the preparation of ellagic acid by acid hydrolysis was obtained, which would provide a reference for the development and utilization of Rosa roxburghii Tratt resources.