Photo-chemical-transformations of organophosphate pesticides, chlorpyrifos, dimethoate and phorate, using advanced oxidation processes (AOPs) namely UV photolysis, UV/H2O2, UV/Fenton and Fenton systems in aqueous solution were investigated in this work. A laboratory set-up was designed to evaluate and select the optimal oxidation process. Results show that addition of hydrogen peroxide/Fenton's reagent increased the UV degradation rates of all pesticides, and data were simulated through kinetic modeling. Kinetic results evidence pseudo first-order degradation, with the rate constant of reaction as 3.3 × 10–4, 2.07 × 10–2 and 1.88 × 10–2 for chlorpyrifos, dimethoate and phorate, respectively. Furthermore treatment efficiencies obtained for the studied AOPs indicate that UV/Fenton was most efficient for chlorpyrifos (50.3% degradation) and UV/H2O2 for dimethoate (96.9%) and phorate (89.6%). Finally, the identification of degradation products indicated that the UV/H2O2 technique results in the formation of fewer end products, with low toxicity. However, UV irradiation of phorate results in information of more toxic degradation end products such as phorateoxonsulfone.