A simple, rapid and direct approach to isocarbophos determination was developed based on the fluorescence quenching of oil-soluble CdSe quantum dots by isocarbophos. Under the optimized conditions, the linear range of oil-soluble CdSe QDs fluorescence intensity versus the concentration of isocarbophos was 2.30×10－7～1.09×10－5 mol·L－1, with a correlation coefficient of 0.999 9 and a limit of detection of 1.1×10－7 mol·L－1. The proposed method has been applied to the determination of isocarbophos in rice and wheat flour with standard recoveries of 93.3%～105.0%. The fluorescence quenching mechanism was further investigated by using UV-Vis absorption spectra and time-resolved fluorescence spectrum. The results indicated that the fluorescence quenching of oil-soluble CdSe QDs by isocarbophos was caused by the change of the surface state which resulted in the enhancement of the surface defect and the occurrence of the non-radiational recombination.