Abstract: A method based on rapid resolution liquid chromatography-tandem mass spectrometry (RRLC-MS/MS) was developed for qualitative and quantitative detection of diethyl maleate in cosmetics. The sample was ultrasonic extracted in 60 ℃ by acetonitrile, then qualitative and quantitative analyzed by RRLC-MS/MS with MRM model. The retention time of diethyl maleate is 2.1 min. The calibration curve is linear in the range of 0.06—20.0 mg/L with R>0.996. The detection limit is 0.1 mg/kg, and the quantitative limit is 0.3 mg/kg. The recoveries of diethyl maleate are in the range of 86.2%—96.4 % with spiked level of 0.5 mg/kg and 5.0 mg/kg. The inner-day precisions of diethyl maleate are 3.19%—8.18%, and the inner-day precisions are 3.72%—7.64 %(n=6). The method is suitable for the standardized determination of diethyl maleate in sunscreen, nail polish and perfume cosmetics.