A rapid quasi-deterministic quantitative method for the determination of 3-methyl-quinoxaline-2-carboxylic acid (MQCA) residues in olaquindox metabolites of animal-derived foods was developed, by using liquid chromatography-tandem mass spectrometry (LC-MS/MS). The sample tissue was extracted by alkaline hydrolysis to extract MQCA, purified by anion solid phase extraction column, and detected by LC-MS/MS, and then quantified by internal standard method. The results showed that MQCA had a good linear relationship in the concentration range of 0.5～50.0 ng/mL, and the correlation coefficient was 0.999 7. The detection limit of MQCA was 0.1 μg/kg. The recovery rate was 95.6%～108.2% at the addition level of 0.1, 0.2 and 1.0 μg/kg, and the relative standard deviation was 3.4%～14.3% (n=6). In conclusion, the detection method above was accurate， rapid and sensitive, and suitable for detecting and confirming the residual amount of MQCA in animal foods.