Abstract: It was shown by the results of a comparative study between GC-NCI-MS and GC-EI-MS on their analytical parameters of selected ions,mass spectrograms,linearity ranges and detection limits,that in their application to the determination of 11 pesticide residues in vegetables,besides diazion and o,p′-DDT,less fragment ions,wider linearity ranges and much lower detection limits (at least 10 times lower) were obtained by GC-NCI-MS,and in addition,in the analysis of a same sample,less foreign peaks were observed.In the determination of pesticides in the molecules of which contained easy electron gaining functional groups,it was preferrable to used the GC-NCI-MS for better sensitivity and selectivity.