A high performance liquid chromatography-quadrupole ion mass spectrometric（HPLC-QTRAP-MS/MS） method was developed for the determination of N-Methyl-o-phenylenediamine residues in telmisartan.After extracted with water-acetonitrile（80∶20，by volume），the telmisartan samples were separated on an Agilent Eclipse XDB-C18 column（3.5 μm,2.1 mm×100 mm） with a mobile phase of 0.1% formic acid solution-acetonitrile.The electrospray was operated in the positive mode and the samples were monitored under the select reaction monitoring（SRM） mode.As a result，the calibration curves of N-Methyl-o-phenylenediamine showed a good linearity（r>0.99） in the range of 2.0-50 μg/L.The limits of detection（S/N=3） was 0.5 μg/L ，and the limits of quantitation（S/N=10） was 2.0 μg/L.The method has the advantages of simple operation，high sensitivity，good reproducibility，and could be used for the detection of N-Methyl-o-phenylenediamine residues in telmisartan.