Abstract: The alogrithm of principle component regression (PCR) was applied to simultaneous spectrophotometric determination of residual amounts of carbaryl (CBR) and isoprocarb (IPC) in food and water.The pesticides,CBR and IPC in sample,were hydrolyzed in alkaline solution,the products obtained were then reacted with the positively charged quinol imide,produced by oxidation of the nitrogen atom in p-aminophenol molecule by potassium periodate,to give 2 respective blue colored compounds,the absorption spectra of which were over lapped seriously.Data of absorbances of sample solution were collected at intervals of 1 nm when scanning in the wavelength range from 500-750 nm.Values of 1st derivative of the data collected were treated according to the PCR algorithm (DPCR) with MATLAB 6.1.Linear relationship was obtain in the range of 0.4 to 4.0 mg per L for both of the pesticides,and the detection limit found were 0.15 mg·L-1 for CBR and 0.20 mg·L-1 for IPC.The proposed method was applied to the analysis of 6 kinds of samples,including food and water;results of recovery test obtained were in the range of 98.4% to 108.4% (for CBR) and of 91.6% to 101.7% (for IPC).