The effective performance of electrocoagulation (EC) technique in the treatment of olive mill wastewater (OMW) was investigated using Al and Fe electrodes. Current densities (CD), electrode materials (Al and Fe), electrolyte amounts, time and initial pH value were selected as parameters. In these parameters, the removal percentage of chemical oxygen demand (COD), color, phenol and lignin from OMW were experimentally investigated. OMW was used directly without pH adjustment and pretreatment. The experiment results show that the removal efficiency depends on time, types of electrodes, applied current and electrolyte amounts and pH value. Optimum working pH was found to be in the range from 3 to 7.