Abstract: An analytical method for the determination of Nε-(1-carboxymethyl)-L-lysine (CML) and Nε-(1-carboxyethyl)-L-lysine (CEL) in fired vegetable oils has been developed using high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS).The sample pretreatment conditions, the chromatographic conditions, and the mass spectrometry conditions were optimized carefully. The optimized conditions were as follows:0.1% formic acid-water solution was used as the extraction solvent, and after shaked extraction for 10 minutes and centrifugation at 3 950 r/min for 4 minutes, the supernatant was collected. The extraction process was repeated once more, the twice extracts were combined, and the final volume was adjusted to 20 mL. 10 mL of the extract was accurately removed with mixed mode cation exchange (MCX) solid-phase extraction (SPE) cartridges which was well activated, then the solid-phase extraction (SPE) cartridges was washed with 3mL water and methanol in turn to drain the column. Finally, the solid-phase extraction (SPE) cartridges were eluted with 5 mL 5% ammonia and methanol. The eluate was concentrated by nitrogen blowing, and then the dried sample was dissolved with 1 mL acetonitrile water (90:10, V/V). The extract was finally detected by tandem mass spectrometry with the multiple reaction monitoring (MRM) acquisition mode. Isotope internal standard method was applied to accurately quantify CML and CEL in fired vegetable oils. Good linear relationships (R=0.999 5) for CML and CEL were obtained in the concentration range of 2.5-100 ng/mL. In the case of 6 determinations per level of addition, the average recoveries at different levels of 5.0, 10.0, and 100.0 μg/kg were in the range of 91.8%-105.4% with the relative standard deviations of 2.8%-7.8%. The CML and CEL limits of detection (LODs) were 2.0 μg/kg, and the CML and CEL limits of quantitation (LOQs) were 5.0 μg/kg. The method provided a fast and efficient way for the determination of CML and CEL in fired vegetable oils.