Membrane separation technology, for bioactive compounds separation, gained great attention lately. Our main goal in this work was to produce an oleuropein concentrate. The water extract of olive leaves has been subjected to a screening on the basis of molecular size. First microfiltration process (0.2 mu m) allowed large particles removal, a following step of ultrafiltration permitted the removal of molecules larger than 5 kDa, finally a nanofiltration process (300 Da) allowed the concentration of polyphenols mainly oleuropein. Permeate fluxes of ultrafiltration and nanofiltration were investigated and analyzed. Results revealed that a large portion of phenolic compounds were recovered in the permeate fraction of the OF process. The nanofiltration retentate showed high polyphenol and flavonoid contents. Based on the content of solute in feed and retentate fractions of NF membrane, oleuropein was concentrated approximately 10 times to reach 1685 mg/100 g extract. In addition, this fraction demonstrated high antioxidant capacities monitored by total antioxidant capacity and ferric-reducing ability power. High antibacterial activity was observed against S. enterica and K. pneumonieae (25 and 28 mm, respectively). (C) 2016 Elsevier B.V. All rights reserved.