Abstract: Objective To establish a method of ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) for determination of residues of eight penicillins in milk products. Methods Samples of milk products were extracted by water in super-sonic instrument. Proteins in the extract were precipitated by acetonitrile and degreased by n-hexane with liquid-liquid extraction, then the purified solution was concentrated by nitrogen, dissolved with acetonitrile-water (10+90,v/v) and cleaned by 0.22 μm millipore filter. The filtrate was separated on a Endeavorsil C18 column by gradient elution in 13 minutes with acetronitrile-water (containing 0.1% formic acid) as mobile phase. Eight penicillins in milk products were detected by UHPLC-MS/MS, identified by electrospray ionization in positive mode using multiple reaction monitoring, and quantified with external standards. Results The calibration curves of residues of eight penicillins showed good linearity in the range of 1.0-100.0 μg/kg with correlation coefficient in the range of 0.999 2-0.999 8. The detection limit of the method was from 0.03 μg/kg to 0.15 μg/kg. The recoveries at three spiking levels ranged from 91.0% to102.3%, and relative standard deviations in the range of 1.02%- 6.13% were obtained. A total of 78 samples of milk powder, liquid milk, fresh milk, and milk beverage were analyzed. Three samples were proved to contain penicillin G in the range of 0.2-1.6 μg/kg. Conclusion The method was applied to determine residues of eight penicilins in milk products by UPLC-MS/MS and proved to be simple, rapid, and accurate, and meet the requirements of monitoring of penicillin in milk products.