A liquid chromatography-tandem mass spectrometric method was developed for the determination of ｏ-tyrosine in γ-ray irradiated protein-rich food.The sample was homogenized and hydrolyzed with parenzyme at 37 ℃ for 24 h.The digestion solution was purified with n-hexane eliminating fat，deproteinated with zinc acetic acid solution，and then determined by HPLC-MS/MS.The quantitation limit was 0.1 mg/kg.The recoveries of ｏ-tyrosine at three spiked levels of 0.1，0.5 and 1.0 mg/kg were in the range of 80%-97%，with RSDs（n=6） of 6.3%-12.9%.The ｏ-tyrosine contents in chicken，pork，beef，fish and shrimp irradiated with 2，5,10 kGy of γ-ray ranged from 0.095 mg/kg to 0.677 mg/kg，which were obviously higher than those in the unirradiated meat samples,and presented linear relationships with the irradiance dose.The method showed good reproducibility and sensitivity.