An ultra-high performance liquid chromatography-tandem mass spectrometry method was developed and validated for the analysis of aflatoxin M_1in milk.Methods Samples were extracted and cleaned by SPE cartridge. Extracts were analyzed for aflatoxin M_1by LC-MS/MS in a single injection with positive electrospray ionization (ESI) mode for aflatoxin M₁. Results Recoveries were 94.8%-98.2% in the range of 0.1-10.0 ng/ml with RSDs less than 3.87%. The limit of quantification was 0.005 μg/kg.Conclusion This essay provides an effective way to detect aflatoxin M1 in milk.