Abstract:  A comparative study was made on three different defined method detection limits ( MDL or LOD ),i.e. simple signal to noise ratio,EPA,and EU/IUPAC(Ccα) methods,for the determination of multi-organophorous pesticides residues such as methamidaphos,acephate,dimethoate,methyl parathion and chlorpyrifos in vegetables. Detailed estimation procedures,group data for various defined“ Method Detection Limit” and brief comments and discussion on each method are given. It is suggested that an appropriate defined method detection limit for method validation and evaluation should be chosen according to the objective of the determination so as to achieve the best economics and reasonable comparison with related international regulations. The results from this study show that an average recovery of 70%～120% with relative standard deviation less than 13% is achieved for the spiking levels of 0.1mg/kg to 0.5mg/kg. For methamidaphos,acephate,dimethoate,methyl parathion and chloryrifos,the method detection limit (MDL) or limit of detection (LOD) for this method as defined by two times signal to noise ratio in reagent blank and in Chinese cabbage matrix is 0.007,0.007,0.002,0.003,0.002 and 0.01,0.009,0.009,0.009,0.008mg/kg,respectively,or by EPA(in Chinese cabbage matrix) is 0.01,0.01,0.01,0.01,0.009mg/kg,and the Ccα as defined by EU and IUPAC(in Chinese cabbage matrix) is 0.02,0.02,0.02,0.02,0.01mg/kg,respectively. The results also show that the Ccα for various pesticide residues in this work could satisfy the more severe demands set by EU 2003/118/EC.