Abstract: OBJECTIVE To establish a method for rapidly detection of ranitidine, phenformin, piroxicam and diclofenac sodium illegally added in Chinese patent medicine by UHPLC-Q-TOF-MS. METHODS The Agilent ZORBAX SB C₁₈(2.1 mm×100 mm, 1.8 μm) column was used, with the mobile phase of methanol-10 mmol·L^-1 ammonium acetate (containing 0.1% formic acid) by gradient elution. Electrospray ionization(ESI) source was used in a positive ion mode, the qualitative and quantitative analyses of the four illegally added substances were combined with retention time, mass spectra, tandem mass spectra and database. RESULTS Ranitidine and phenformin were detected illegally added in Baicaotang capsules. Ranitidine, piroxicam and diclofenac sodium were detected illegally added in Mengshi Kechuanling capsules. CONCLUSION This method is accurate, efficient, rapid and can be used to detect the ranitidine, phenformin, piroxicam and diclofenac sodium illegally added in Chinese patent medicine.