To compare the effects of processing on free anthraquinones which were the main active ingredient in Semen Cassiae. Methods:The content of six free anthraquinones in Semen Cassiae was determined by the high-performance liquid chromatographic method and compares the content changes before and after processing. The six free anthraquinones were aurantio-obtusin, rhein, obtusifolin, emodin, chrysophanol and physcion. Results There was no significant difference in the content changes of aurantio-obtusin and rhein, and the content of obtusifolin was increased by 25%. The content of emodin was increased by 21%, and the content of chrysophanol was decreased by 15%. The content of physcion was decreased by 21% after processing. Conclusion:Processing has different effects on the content of free anthraquinones. Some free anthraquinones contents remained unchanged while some increased significantly, and some decreased significantly.