Abstract: A method for the simultaneous determination of the ochratoxins A,B and C in cereals and its products by high-performance liquid chromatography-tandem mass spectrometry(HPLC-MS/MS)with isotope internal standard was established. Samples were extracted by acetonitrile-water(84:16,V/V),after shocked and centrifuged steps,the supernatant were enriched and purified through the immunoaffinity column of ochratoxin. Finally the supernatant was detected by HPLC-MS/MS method using Waters ACQUITY BEH C₁₈(50 mm×2.1 mm,1.7 μm),and analyzed by multiple reaction monitoring(MRM)mode under positive electro-spry ionization(ESI⁺)with internal standard method. This method was quantified by OTA-¹³C₂₀,which used as an internal standard. Results showed that,under the optimized conditions,ochratoxin A,B and C showed good linearity in the linear range of 0.25~2.5 ng/mL,and the determination coefficients were all above 0.999.The limits of detections(LODs,S/N=3)and the limits of quantification(LOQs,S/N=10)were 0.003~0.018 μg/kg and 0.011~0.059 μg/kg,respectively. The recovery rates of 3 kinds of cereals and its products with 3 spiked levels(2.0~10.0 μg/kg)were 80.50%~107.08%,and the relative standard deviations(RSDs)were 0.14%~4.94%(n=6). When ten samples were tested by this method,only one sample was detected of OTA with the content of(0.35±0.01) μg/kg. This paper proposed a method which is simple and easy,sensitive and suitable for determination of ochratoxins in cereals and its products.