Abstract: A method was proposed for the determination of sterigmatocystin in plant food with isotope diution internal standard by HPLC-MS/MS. Sample of plant food was extracted with a mixture of acetonitrile and water. The extract was purified on HLB SPE microcolumn. The purified extract was concentrated and then separated on RP-LC column. ESI and MRM were adopted in MS/MS analysis and isotope dilution internal standard was used for quantification. Linearity range for sterigmatocystin was found between 0.5-100 μg·L-1 with correlation coefficient greater than 0.999. Values of lower limits of determination (10S/N) found for wheat and maize were same to be 0.5 μg·kg-1, and for peanut and soybean were same to be 0.8 μg·kg-1. Standard sterigmatocystin of different concentration levels was added to various matrixes of plant food, and tests for recovery were made, giving values of recovery in the range of 88.2%-105%. Values of intra-day RSDs (n=6) found were less than 7.5% and of inter-day RSDs (n=3) found were less than 9.0%.