A method for the determination of dicyandiamide (DCD), melamine (MEL) and cyanuric acid (CY) in milk and milk powder has been developed by ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). After extracted by 5% (mass fraction) trichloroacetic acid, the samples were loaded onto an Acquity UPLC HSS T3 column (50 mm x 2.1 mm, 1.8 microm) and separated using acetonitrile and ammonium acetate as mobile phases in a gradient elution mode. The electrospray was operated in the positive mode and negative mode, and monitored by the multiple reaction monitoring (MRM) mode. The calibration curves showed a good linearity in the range of 5.0 - 200.0 microg/L, and the correlation coefficients (r) were not less than 0.995. When the spiked levels were 0.02, 0.10 and 0.20 mg/kg, the recoveries of DCD, MEL and CY in milk ranged from 60.0%. to 105.8%, with the relative standard deviations (RSDs) of 4.2% - 13.6%; while the spiked levels were 0.05, 0.10 and 0.20 mg/kg in milk powder, the recoveries ranged from 78.0% to 115.0% with the RSDs of 2.7% - 7.5%. The limits of quantification (LOQs, S/N = 10) were 0.02 mg/kg for milk samples and 0.05 mg/kg for milk powder samples. The results indicate that the method is simple, rapid, sensitive and suitable for the qualitative and quantitative analyses of DCD, MEL and CY in milk and dairy product samples.