The present study investigates the removal of pesticide by electro coagulation process. A glass tank in 1.56L volume with four iron plate electrodes was used to perform the experiments. The electrodes connected to a DC power supply (bipolar mode). The tank was filled with synthetic wastewater were which contained diazinon pesticide in concentration of 10, 50 and 100 mg/L. The percent of diazinon removal was measured at pH= 3, 7 and 10 and in electric potential range of 20-40V by thin layer chromatography method. The results indicated that initial concentration of diazinon can affect efficiency removal and for higher concentrations of diazinon, higher electrical potential or more reaction time is needed. The results showed that for a given time, the removal efficiency increased significantly with increase of voltage. The highest electrical potential (40V) produced the quickest treatment with >99% diazinon reduction occurring after 60 min. The final pH for iron electrodes was always higher than initial pH. Finally it can be concluded that electro coagulation process (using iron electrodes) is a reliable, efficient and cost-effective method for removal of diazinon from aqueous environments, especially designed for pH=3 and voltage=40V.