Objective,Used the TG/DTA curves and XRD patterns to identify five kinds of free anthraquinones.Method,The thermograms,differential thermograms and X-ray powder diffraction patterns were obtained by thermal analyzer and X-ray powder diffraction analyzer.Result,By analyzing the TG/DTA curves and XRD patterns of the free anthraquinones(Rhein,Emodin,Aloe-emodin,Chrysophanol and Physcion)from Rheum,the results showed that they had the similar TG curves,however,due to the substituents attached on the 1.8-dihydric anthraquinones are different,every sample had different weight lose.All the DTA curves of free anthraquinones had two obviously characteristic peaks,but there were obviously differences on curvilinear shapes,peak location and peak values.The X-ray powder diffraction patterns of free anthraquinones have their own characteristic and very obvious.Conclusion: According to the differences in the thermal and XRD properties of five free anthraquinones,the kind of free anthraquinones could be easily identified and they can be used as correspondence free anthraquinones’s characteristic fingerprint patterns.