Abstract: The stability of traloxydim in acetonitrile, methanol and acetonitrile-2% acetic acid (80 : 20, V/V) was investigated under different conditions. The traloxydim standard solution was stored at 25 ℃, 40 ℃, 60 ℃, and sampled at intervals in 24 h. Qualitative and quantitative analysis were established through ultra-performance liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS) and high-performance liquid chromatography coupled with diode array detection (HPLC-DAD), respectively. The stability of traloxydim was evaluated by analyzing the isomer ratio and inversion rate of the oxazole product. The results showed that tralkoxydim existed as planar enol forms of E-isomer and Z-isomer, and predominated by the former isomer. The stability of traloxydim was closely related to the solvent and the storage temperature. Traloxydim was stable in acetonitrile and no degradation was observed. In methanol and acetonitrile-2% acetic acid (80 : 20, V/V), the isomerization fromE-isomer to Z-isomer was detected in rapid equilibrium. Furthermore, tralkoxydim underwent Beckmann rearrangement by the loss of ethanol to give more oxazole products at high temperature and polar solvents. Therefore, acetonitrile was suitable to be the solvent and mobile phase of tralkoxydim, and low temperature contributed to the improvement of its stability in the solution.