A new and highly sensitive spectrophotometric method is developed for the determination of carcinogenic pesticides dichlorvos. The method is based on alkaline hydrolysis of dichlorvos to dichloroacetaldehyde, which react with p-nitroaniline in alkaline medium. The absorption maxima of the yellow dye is measured at 455 nm. Beer’s law is obeyed over the concentration range of 10 to 90 µg in a final solution of 25 ml (0.4-3.6 ppm). The molar absorptivity, Sandell’s sensitivity and correlation coefficient were found to be 2.3x104 l mol-1cm-1, 0.013 μg and 0.9989 cm-2, respectively. The method is simple, sensitive and free from interferences of other pesticides and diverse ions. The method has been satisfactorily applied to the determination of dichlorvos in vegetable and water samples.