Abstract: A analytical method for the determination of phenylethanolamine A in feed by high performance liquid chromatography-tandem mass spectrometry was established. The samples were extracted with 80% (V:V) acetonitrile aqueous solution. After purified by PRiME HLB, the samples were determined by high performance liquid chromatography-tandem mass spectrometry and quantified by external standard method. Then, the gradient elution was performed through Hypersil GOLD C18 chromatographic column (1.9 μm, 2.1 mm×100 mm) by using 0.1% formic acid aqueous solution and methanol as the mobile phase. And the qualitative and quantitative analysis was carried out by using the modes of electrospray ionization (ESI⁺) and positive-ion scanning multiple reaction monitoring (MRM). The results showed that phenylethanolamine A had a good linear relationship in the range of 5.0~200.0 ng·mL^-1 (r=0.999 2). The recoveries were 82.2% to 91.5% at the supplemented levels of 10.0, 20.0 and 50.0 μg·kg^-1, the relative standard deviations (n=6) were 6.8% to 8.5%, the limits of detection (the SNR being greater than 3) were 0.1 μg·kg^-1, and the limits of quantification (the SNR being greater than 10) were 0.3 μg·kg^-1. The method had good precision and high sensitivity, and could be used for the rapid and accurate determination of phenylethanolamine A in large quantities, which would effectively improve the work efficiency.