In this study, treatability of olive mill wastewater (OMW) by acid cracking, chemical coagulation, and Fenton process was investigated. Various coagulants, such as alum, ferric chloride, ferrous sulfate, and bentonite were examined in chemical coagulation process and the chemical oxygen demand (COD), total phenols, color, and aromaticity were determined. The removal of COD, color, total phenols, and aromaticity in acid cracking were 47, 63, 30, and 57%, respectively. The pH, iron-salt, and hydrogen peroxide dosage were found to significantly affect the efficiencies of Fenton process and acidic pH conditions were the most effective. Acid cracking and Fenton process showed high efficiency of COD (83%), total phenols (98.6%), color (77%), and aromaticity (67%) removal from the OMW. As a result of this study, acid cracking and Fenton process have a significant effect in reducing the COD and total phenols from OMW.