Abstract: A method for detection of adulteration in milk containing nonprotein nitrogen by infrared spectroscopy was established. Through adulterating different content of urea and melamine into pure milk, the infrared spectral data of the samples were obtained by the Nicolet 6700 FT-IR Spectrometer, followed by water background correction and milk background correction to carry on processing the spectrum data, the characteristic peaks of urea and melamine were obtained. Combining the different MATLAB program with the wavenumber, the absorbance value or the peak area of characteristic peaks, the adulterants in milk could be judged. The method could be used for quantitative and qualitative analysis of adulterants. The correct recognition rate was95.49%, the relative error was within 2%. This method was fast, simple and suitable for determination of different nonprotein nitrogen.