In the current research, the surface of a polyethersulfone (PES) nanofiltration membrane was modified by polyvinyl alcohol (PVA) and iron-oxide nanoparticles (Fe3O4) through a crosslinking reaction with glutaraldehyde (GA). The effect of the coating layer on the morphology, physico-chemical properties, separation and antifouling performance of the membranes was studied. The analysis of FTIR spectra, scanning electron microscopy (SEM), atomic force microscopy (AFM), porosity and mean pore size measurement, contact angle analysis, salt rejection and filtration of a powder milk solution was the basis of membrane characterization. Surface and cross-sectional SEM images showed the formation of a dense layer on the PES based NF membrane after coating. The pure water flux, porosity and mean pore size were decreased; the water contact angle was slightly lower due to the hydrophilic nature of PVA and Fe3O4 nanoparticles. The surface roughness initially decreased for a coating with a low concentration of nanoparticles but increased when a higher amount of nanoparticles was used. The salt rejection significantly increased from 68.4% for a bare PES membrane to 94% for the modified ones (sample 6) by surface modification. Filtration of a powder milk solution revealed the best antifouling performance for the membrane modified by PVA/Fe3O4 (2 wt %). (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.