Abstract: To investigate the degradation of enantiomers of myclobutanil in tomato (Lycopersicon esculentum Mill.) fruits under field conditions, the separation of myclobutanil enantiomers and the enantioselective degradation in toamto were studied using a chiral Lux Cellulose-1 column separation and ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The samples were extracted by acetonitrile and purified with QuEChERS. The method showed reliable performances in linearity, recovery and precision. The correlation coefficient of calibration curves were over 0.99 in the range of 0.000 5 to 0.05 mg/L, the average recoveries of myclobutanil enantiomers in tomato varied from 92% to 96% with the relative standard deviation (RSD) ranging from 1.0% to 3.0% at 0.005, 0.05 and 0.25 mg/kg spiked level. Results of degradation trials indicated that the degradation of enantiomers of myclobutanil in tomato fruits followed to the first-order reaction kinetic equation. And the half-lives of myclobutanil enantiomers ranged from 2.77 d to 4.08 d. The degradation of myclobutanil enantiomers in tomato fruit exhibted significant selectivity. The enantiomer fraction (F_E) values decreased with time from 0.47 to the minimum of 0.24. S-(+)-Myclobutanil was more susceptible to degradation in tomato, which resulted in the relative enrichment of R-(–)-myclobutanil. The degradation of myclobutanil in tomato was evaluated from the perspective of enantiomers, and the results of this study would provide the basic data support for the risk assessment of myclobutanil in agricultural products.