Abstract: An analytical method of GC-MS/MS was established for the simultaneous determination of 3-cyanobenzyl bromide and 4-cyanobenzyl bromide in 2-cyanobenzyl bromide used in aglitine benzoate. The method was performed on a VF-17MS capillary column (50% benzene-50% dimethylsiloxane copolymer, 30 m×0.25 mm, 0.25 μm). The column temperature was risen by program. The injector temperature was controlled at 260℃. The analytes were detected with MS/MS in multiple reaction monitoring (MRM) mode. The method was found to show good linearity with regression coefficients all more than 0.998 0. The limits of detection (3S/N) all were 2.0 μg·L^-1. The recoveries of 3-cyanobenzyl bromide were 92.1%-97.0%. And the recoveries of 4-cyanobenzyl bromide were 102%-109%. The test solution, reference solution and system suitability solution were stable for at least 18 h at 25℃. No 3-cyanobenzyl bromide and 4-cyanobenzyl bromide were detected in three batches of production scale samples. With high sensitivity, good resolution and accuracy, the method could be reliably and effectively used in the determination of the above two kinds of trace impurities in 2-cyanobenzyl bromide. This method provides a guarantee for the safety of alogliptin benzoate.