Objective: To establish a high-performance liquid chromatog.-mass spectrometry (LC-MS/MS) method for the determination of the genotoxic impurity 2-(2-oxo-1-phenyl-5-(N-pyridine oxide)-2-yl-1, 2-dihydropyridine-3-yl) benzonitrile in perampanel.Methods: The chromatog. conditions were as follows: a C18 column (YMC-Triart C18, 2.1 mm×100 mm, 1.9 μm) using 0.05% formic acid aqueous solution ( mobile phase A) and acetonitrile (mobile phase B) in gradient elution (0∼1 min, 10%B; 8∼10 min, 90%B; 10.1∼12 min, 10%B).The flow rate was 0.3 mL/min, injection volume was 5 μL.The mass spectrometry conditions were as follows: electro spray ionization source (ESI+), multistage reaction monitoring (MRM) mode, ion spray voltage of 5500 V, ion source gas pressure of 344.74 kPa (50 psi), curtain gas pressure of 50 344.74 kPa (50 psi), auxiliary heating gas pressure of 50 344.74 kPa (50 psi), drying gas temperature is 500°C, carrier gas flow of 500 L/h, declustering potential of 150 V, collision energy of 27 V, monitoring ion pair of 366.0→273.0 and scanning time of 100 ms.The 0∼6.8 min HPLC eluent was entered into the mass spectrometry for detection, and the 6.8∼12 min HPLC eluent was cut into the waste.Results: 2-(2-oxo-1-phenyl-5-(N-oxidepyridine)-2-yl-1, 2-dihydropyridine-3-yl) benzonitrile had good linearity in the range of 3.76∼18.80 ng/mL (r=0.9989), the limits of detection and quantification were 1.13 and 3.38 ng/mL, resp., and the recovery rate was 85.9%∼94.2%, with good stability.It has strong specificity and is suitable for the determination of 2-(2-oxo-1-phenyl-5-(N-oxopyridine)-2-yl-1, 2-dihydropyridine-3-yl) benzonitrile content in perampanel.