Abstract: A liquid chromatography-tandem mass spectrometry（LC-ESI-MS/MS）method for the determination of melamine and its analogues (CYA, AMD, AMN) in feeds & soils was reported. The analytes were extracted with the soluction （V（2.5% formic acid）∶V（acetonitrile）=50∶50） from matrix, and then the extracting solution was evaporated by nitrogen blow, dissolved in the soluction （V（0.2% formic acid）∶V（acetonitrile）=10∶90） and assayed by LC-MS/MS. The chromatographic retention time and mass fragment ion abundances ratio for qualitative, and with ¹⁵N₃-melamine, ¹³C₃-cyanuric acid as internal standard for quantitative. Scanning of positive ions and negative ion scan the instrument method studies, to determine the abundance ratio of the highest two pairs of ions as monitoring ion MRM mode for qualitative and quantitative analysis. The limit of detection (LOD) is 0.25—0.50 mg/kg. The correlation coefficient is greater than 0.999 within the linear range of 5.0—500.0 μg/L. Recoveries of MEL, CYA, AMD and AMN are 61.4%—115%, and the relative standard deviation is less than 12.6% at spiked levels of 0.5—2.0 mg/kg (n=5).