A simple and sensitive method was developed for the determination of ethephon residues in cotton seed,cotton leaf and soil by solid phase extraction/ultrahigh performance liquid chromatography-tandem mass spectrometry(SPE/UPLC-MS/MS).The samples were extracted with methanol-01% formic acid,purified with an Oasis MAX column,and separated on a Cortecs Hilic column,finally analyzed in multiple reaction monitoring(MRM) mode via negative electrospray ionization(ESI-).Under the optimum condition,the calibration curves for the analyte were linear in the range of 0.02-1.94 mg/L,with correlation coefficients(r2) not less than 0.996 3.The limits of detection and quantitation for ethephon were 0.01 and 0.02 mg/kg,respectively.At spiked levels of 0.02,0.194 and 3.88 mg/kg,the recoveries for ethephon in three matrices were in the range of 78.3%-95.1% with relative standard deviations(RSDs) of 1.9%-5.2%.With the advantages of simplicity,high sensitivity,and good repeatability,the method could satisfy the requirements for determination of ethephon in cotton seed,cotton leaf and soil.