Abstract: Objective: To identify Phenolphthalein illegally added to diet pills by Raman spectroscopy. Methods:Raman spectroscopy was used to identify Phenolphthalein added to diet pills. First,diet pills were extracted by suitable solvent,then extracting solution were filtered. Finally filtrate were measured by Raman spectroscopy.Results Calibration curve was built and analysis were performed on samples with different content of Phenolphthalein. Results were accordance with real amount added. Conclusion: With suitable sample preprocessing method,Raman spectroscopy could be used to fast screening Phenolphthalein illegally added to diet pills.This method is fast,simple,low cost and can give both qualitative and quantitative results. The detection limit is 1% for Phenolphthalein in diet pill.