Abstract: OBJECTIVE To establish a LC-MS method for the determination of 8 chemicals(including theophylline, sulfamethoxazole, prednisone acetate, diazepam, chlorpheniramine, diphenhydramine, pentoxyverine, benproperine) illegally added into cough and asthma traditional Chinese medicine. METHODS A high performance liquid chromatography-ion trap mass spectrometry and electrospray ionization source were adopted to perform the analysis operated in positive and negative ion modes with full scan MS and full scan MS² modes. Chromatographic separation was performed on a SHISEIDO CAPCELL-PAK C₁₈ column(4.6 mm×150 mm, 5 μm) with the mobile phase consisted of acetonitrile-0.02 mol·L⁻¹ ammonium acetate solution by gradient elution at a flow rate of 0.5 mL·min⁻¹. The qualitative identification of chemical components illegally added in samples was performed by comparing the chromatograms and mass spectrograms of the reference substances and samples. RESULTS A good chromatographic resolution of 8 compounds was obtained under the LC-MS condition. Out of 21 batches of samples, 3 samples contained theophylline with the detection limit of the method of 0.1-0.4 μg·mL⁻¹. CONCLUSION The method is simple, selective and rapid. It is suitable for the rapid analysis and detection of 8 chemical substances illegally added in Chinese patent medicines for relieving cough and asthma.