In this study, hybrid nanofiltration (NF) membranes were fabricated by introducing oleic acid-titanium oxide (OA-TiO2) nanoparticles into the polyethersulfone (PES) by phase inversion method. The OA-TiO2 nanoparticles were synthesized and then different concentrations of synthesized nanoparticles were used to prepare NF membranes. The synthesized nanoparticles were characterized by Fourier transform infrared spectroscopy (FTIR), Field emission scanning electron microscopy (FESEM), and X-Ray Diffraction analysis (XRD). Moreover, the morphology of membranes was investigated by FESEM, the energy dispersive X-ray (EDX) analytical method, atomic force microscope (AFM) analysis. The separation performance of membranes was evaluated by the contact angle, pure water flux (PWF), flux recovery ratio (FRR%), and the rejection of Na2SO4 and Cu(NO3)(2). The highest PWF (18.206 L/m(2)h) was obtained to PES-based membrane containing of 0.05 wt.% OA-TiO2 nanoparticles with a 42% increase compared with the pristine PES membrane at operating pressure of 4.5 bar due to increasing membrane hydrophilicity and better dispersion of OA-TiO2 nanoparticles. Furthermore, the best Na2SO4 rejection (81.5%) was obtained to membrane containing of 0.1 wt.% of OA-TiO2 nanoparticles and the highest Cu(NO3)(2) removal (79%) was revealed to membranes containing of 0.5 wt.% OA-TiO2 nanoparticles that showed the increase of 21% and 25% compared to the pristine PES, respectively. The enhancement of salt rejection attributed to electrostatic repulsion and adsorption mechanisms. The incorporation of OA-TiO2 nanoparticles into the PES enhance FRR% to 83% that led to improving anti-fouling properties. (C) 2020 Published by Elsevier B.V. on behalf of Institution of Chemical Engineers.