Background & Objective: Nowadays petroleum compounds have been widely used all over the world. Intentional and accidental release of these compounds into the environment disturbs aquatic ecosystem especially groundwater. Therefore, removal of petroleum compounds from water is necessary from the point of health and environmental view. This work aimed at investigation of the effect of electro-coagulation process using iron and stainless steel electrodes on removal of petroleum compounds from groundwater. Methods: required water samples were taken from one of the monitoring wells of Tehran petroleum refinery. Effect of electro-coagulation process using iron and stainless steel electrodes on removal of petroleum compounds was evaluated through determination of turbidity and COD in groundwater. The variables studied include the effects of current density, anode and cathode types, reaction time, and initial pH of solution. Turbidity was measured using a HACH 2100 N TURBIDIMETER and COD was determined by open reflex method. Results: The optimum materials for anode and cathode were determined to be stainless steel and Iron, respectively. Efficiency of process was improved by increasing current density and reaction time. The optimum pH was found to be between 7 and 9. Conclusion: The results obtained imply that the electro-coagulation would be an efficient and reliable technique for removal of petroleum contaminants from groundwater.