Abstract: A method for the simultaneous determination of benzimidazoles and their metabolites in dairy products was established using ultra high performance liquid chromatography-tandem mass spectrometry (MS). After extracting the samples with acetonitrile containing 0.2% formic acid, the extracts were centrifuged and purified by solid phase extraction column, and then separated by UPLC HSS T₃ chromatographic column, determined in multi reaction monitoring (MRM) method with a positive ESI mode. The results showed that the linear correlation coefficient (r) within the range of 1.0~50 μg/L was greater than 0.995 (except for trichlorophenyl-dazoxazole, which was 0.9578). The method had a limit of detection (LOD) of 0.002 mg/kg (except for albendazole-2-aminosulfone, thiabendazole, and thiabendazole-5-hydroxy, which were 0.003 mg/kg). The limit of quantitation (LOQ) (S/N=10) was 0.005 mg/kg (except for albendazole-2-aminosulfone, thiabendazole, and thiabendazole-5-hydroxy, which were 0.010 mg/kg). The recoveries at three spiked levels of 0.005, 0.01 and 0.05 mg/kg ranged from 62.5% to 117.6%, with relative standard deviations (RSD) between 1.92% and 12.17%. The method is simple to operate, highly sensitive, and suitable for the quantitative analysis of benzimidazoles and their metabolites in dairy products.