Abstract: A rapid method for analyzing the fosetyl-aluminium (Al) residues in Chinese cabbage was developed using ultra-high performance liquid chromatography-tandem mass spectrometry(UPLC-MS/MS). This method quantified the concentration of fosetyl-Al by determining the contents of ethyl phosphonic acid and phosphorous acid. Analytes were detected by electro-spray ionization (ESI-) and multiple reaction monitoring (MRM) mode. Fosetyl-Al dissociated as ethyl phosphonic acid and phosphoous acid, and the ratios between the two acids were 40:60 with different solution. Quantification was performed by peak area external standard methods using matrix-matched calibration curves, which were linear in the range of 10-500 μg/L with good linear relationships. The correlation coefficients were better than 0.999. The limit of quantification (LOQ) of fosetyl-Al was 1.3 μg/kg. At 0.01, 0.10 and 0.50 mg/kg spiked levels, the recoveries and the relative standard deviations (RSD) were 82%-107% and 6.7%-9.2% (n=5) for fosetyl-Al. This method was simple, rapid, accurate, which could be applied to the determination of fosetyl-Al residues in Chinese cabbage.