Abstract: It was proved that either of the method of GC-ECD or of GC-MS/MS was suitable to be used in the determination of residual bentazon in grains.The method of GC-MS/MS gave qualitative and quantitative results simultaneously,and showed better reliability.The method of GC-ECD showed higher sensitivity,and was more effective in quantitative analysis.A common procedure of sample pre-treatment for both of the above methods was proposed.10 g of sample was extracted with methanol,and defatted by extraction with n-hexane.The aqueous phase was acidified to pH≤3 with dil.HCl,and the bentazon was then extracted into dichloromethane,which was evaporated to dryness at 45 ℃ under reduced pressure.The concentrated residue containing the bentazon was dissolved in 0.2 mL CH3OH,methylated and purified by solid phase extraction.The residual bentazon was dissolved in 1 mL of n-hexane,and was ready for use in GC or GC-MS determination.In the analysis of several grain samples by the above mentioned methods,values of RSD in the range of 2.3%-4.7% were obtained for GC-ECD,and of 3.5%-6.7% for GC-MS/MS.Recoveries obtained by standard addition method were in the ranges of 77%-98% and 80%-102% for GC-ECD and GC-MS/MS respectively.The limit of determination was found to be 001 mg·kg-1.