Olive mill wastewaters (OMW) with its physicochemical and microbiological properties is one of the most important problems facing the Mediterranean countries, due to its adverse effects on different ecosystems and because they reject without any treatment. The objective of this work is the treatment of OMW by combining two chemical processes: coagulation-flocculation and oxidation. We are interested in the first step to the physicochemical characterization of vegetable water, in second step to the chemical treatment of OMW by coagulation-flocculation using Jar test method, followed by oxidation with hydrogen peroxide (H2O2). The effluents had a highly acidic pH (4.93) and are loaded on organic matter, very highly polluted and rich on phenolic compounds (COD=112g/l, OD=1.53). To clean the effluent, coagulation- flocculation in optimal condition followed by oxidation by H2O2 can reduce the chemical oxygen demand (COD) to 10g/l (91% of reduction).