The photocatalytic degradation of the organophosphorus insecticide diazinon in aqueous suspensions was studied by using Ni-doped ZnO nanorods as a photocatalyst. The effects of some operational parameters such as solution pH, nanocatalyst dosage, initial diazinon concentration, different purging gases, H2O2 concentration, and type of organic compounds on the removal efficiency were studied. Under optimal conditions: pH=7, [Diazinon](0)=20mg/L, nanocatalyst dosage=0.2g/L, H2O2=15mM, 99.96% of the insecticide was removed after 120min. Three kinetic models were developed for this process, and the findings showed that the diazinon removal rate obeyed the first-order kinetic.