Abstract: In order to strengthen the supervision of the quality of infant formula milk powders which is the main food of infants，δ¹⁵N and δ¹³C of casein in infant formula milk powders were determined by elemental analysis-stable isotope ratio mass spectrometry(EA-IRMS). Casein which purity was over 96%， was extracted from milk powder by isoelectric-precipitation of proteins and identified by nano liquid chromatography & quadrupole-time-of-flight mass spectrometer(Nano LC-QTOF-MS). The ranges of δ¹⁵N and δ¹³C are correlated with the regional origins of infant formula powders. The values of δ¹⁵N and δ¹³C of casein from the milk powders with the same origin are very similar, whereas they are quite different with different origins. It is a reliable and convenient method to determine the regional origin of infant formula powders.