Abstract: An effective method was developed for determination of mesotrione residue in sugar cane and soil. Field trials were designed to evaluate the dissipation and residue of mesotrione in sugar cane and soil at two locations:Guangdong and Guangxi. The samples were extracted by acetonitrile, and further distributed by dichloromethane and detected by high performance liquid chromatography with photo-diode array(HPLC-PDA). The results showed average recoveries of 82%-84% with relative standard deviations of 1.9%-3.4% at spiked levels of 0.01, 0.1 and 1 mg/kg. The limit of detection was 0.005 mg/kg and the limit of quantification was 0.01 mg/kg. It was found that under field trial conditions, residue levels of mesotrione in sugar cane decreased first, then increased, and decreased again. The half-lives ranged from 12.3 to 14.7 days in soil. The terminal residue was all below 0.01 mg/kg at harvest time.