The production of olive oil generates huge quantities of by-product called olive mill wastewater (OMW), which poses serious environmental problems. This effluent contains several polyphenols. In this work, we have studied the liquid-liquid extraction on olive mill wastewater using ethyl acetate. By a colorimetric assay, we revealed that phenolic compounds are very abundant in olive mill wastewater. The evaluation of the antioxidant activity of the extracts confirms its potential to scavenge free radicals under fast kinetic behavior (1-2 min) compared with synthetic antioxidants. The enrichment of olive oil with phenolic fraction was performed showing that the antioxidant activity increases with the increase of phenolic fractions added, allowing the improvement of the antioxidant ability of olive oil. To conclude, our data demonstrate that low-cost natural phenolic extracts retain high antioxidant activity and fast kinetic behavior and can improve the antioxidant activity of olive oil instead of synthetic antioxidants.