Hypothesis: A thin film nanofiltration membrane was modified by poly(vinyl alcohol) (PVA) and chitosan-functionalized activated carbon nanoparticles. The effect of a surface layer formed on the structure and separation properties of prepared membranes was investigated.Methods: Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), water content, porosity and mean pore size measurements, Na2SO4 and NaCl rejection, water flux as well as membrane flux recovery ratio for the study of antifouling ability were used for characterization of the membranes.Findings: The FTIR results confirmed the formation of hydroxyl and amine groups on the surface of modified membranes. The SEM images also showed the formation of a uniform layer on the modified membranes. As shown in the SEM images, adding functionalized activated carbon nanoparticles into PVA leads to a heterogeneous and dense structure on the surface of modified membranes. Modification of pristine membrane by PVA and modified activated carbon nanoparticles up to 0.25% wt initially increased the water content, and subsequently with increase in nanoparticles ratio from 0.25 to 1.0wt%, the water content decreased. The obtained results showed a larger mean pore size for all modified membranes compared to pristine membrane. Moreover, all modified membranes showed a higher flux in comparison with virgin membrane. In addition, salt rejection revealed that the surface modification of nanofiltration membrane has a positive effect in preventing smaller rejection amount despite the increase in the amount of flux. Sodium sulfate salt rejection was also measured more than sodium chloride salt rejection. Flux recovery ratio was also measured more than 92% for the modified membranes whereas it was more than 66% for pristine membrane that confirms the antifouling ability for the modified membranes.