Abstract: A comprehensive analytical method has been developed for the simultaneous determination of mesotrione and its metabolites (4-methylsulfonyl-2-nitrobenzoic acid (MNBA), 2-amino-4- (methylsulfonyl) benzoic acid (AMBA)) in soils by ultra performance liquid chromatography-tandem mass spectrometry (UPLC-ESI-MS/MS). The soil samples were extracted with 0.1% ammonium hydroxide solution/acetonitrile and an aliquot of the extract was cleaned-up by a solid-phase extraction Cleanert PAX cartridge. The chromatographic separation was performed on an Acquity HSS T3 column with gradient elution using acetonitrile and 0.3% formic acid in water. The analytes were measured by multiple reaction monitoring (MRM) in the electrospray negative ionization mode. The recoveries were 73%-97% with the relative standard deviation from 2.4% to 12.9% for spiked soil samples at 0.3 μg/kg- 50 μg/kg. The limits of detection of mesotrione, MNBA and AMBA in soils were 0.1, 0.3 and 0.2 μg/kg, and the limits of quantifications of mesotrione, MNBA and AMBA were 0.3, 1.0 and 0.6 μg/kg. The analytical method has been employed in the simulation experiments with the red soil samples. The result showed that the half-life of mesotrione was 4.0 days in the red soil and the residue amounts of AMBA were higher than MNBA.