Abstract: A method was developed for the quantitative determination and confirmation of chlormequat and difenzoquat using ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The blank water, blank whole blood, blank urine and blank liver were diluted by ammonia water (pH = 8), then vortexed and centrifuged. The supernatant was cleaned-up using Oasis^®WCX solid phase extraction cartridges. Extracts was analyzed by UPLC-MS/MS in positive ionization and multiple reaction monitoring(MRM) mode. The parent ion and two daughter ions of chlormequat and difenzoquat were detected for quantification and confirmation. During the experiments, the degradation rates of standard products under different conditions ranged from 2.4% to 11.9%, and the stability was good. The recoveries of chlormequat and difenzoquat ranged from 71% to 110% with the spiked levels of 0.010, 0.10, 0.25, 0.50 and 1.0 mg/kg. And the relative standard deviation (RSD) ranged from 1.1% to 19%. The limits of quantification (LOQs) of all those herbicides were 0.01 mg/kg. The detection limit was 0.005 mg/kg. This method was proved to be selective, sensitive and rapid.