A method was developed for the determination of dicyandiamide in infant milk powder by high-performance liquid chromatography-mass spectrometry（LC-MS/MS）.The conditions of extraction and parameters of LC-MS were optimized.The sample was extracted with water,precipitated with acetonitrile,then separated on a Thermo syncronis column using mixture of acetonitrile（containing 0.2% formic acid）-0.1% formic acid（containing 10 mmol/L ammonium formate）（95∶5） as mobile phase at a flow rate of 0.3 mL/min.The detection of dicyandiamide was performed by positive-ion electrospray ionization mass spectrometry（ESI-MS） utilizing multiple reaction monitoring of two parent-daughter ion pairs:m/z 85/68 and 85/43.A good linear relationship was obtained in the range of 0.2-100 μg/L,with a correlation coefficient of 0.999 8.The spiked recoveries at different spiked levels were in the range of 79%-83%.The detection limit of dicyandiamide was 0.1 μg/L,and the quantitatiion limit of method was 5 μg/kg.The results indicated that the method was rapid,selective,sensitive and stable enough to examine dicyandiamide in infant milk powder.