The possibility of complete fractionation of olive mill wastewater (OMW) was investigated using membrane technology. Combinations of different membrane processes were used for the fractionation of OMW into by-products that may be further developed to achieve reduction of the expenses involved. Ultrafiltration (UF) in combination with nanofiltration (NF) and/or reverse osmosis (RO) were found to be very efficient for the treatment and fractionation OMW. An extended parametric study for the optimum fractionation yield of OMW involved variation of the operational system parameters including temperature, and the trans-membrane pressure. The final effluent obtained was a clean transparent with very low content of organic compounds and dissolved ionic salts. The chemical composition of the post-treatment effluent showed that it was suitable for disposal in aquatic receptors or for use for irrigation purposes. The ultrafiltration process resulted in the separation of high molecular weight constituents including suspended solid particles. Phenols present in the OMW were removed to an extent exceeding 95% of the initial value following the nanofiltration step. The concentrate obtained at this stage was very rich in phenols. Better efficiency of the OMW treatment was achieved applying RO after UF.