In this study, modification of polyvinyl chloride (PVC) ultrafiltration membranes with zinc oxide (ZnO) nanoparticle addition was taken into consideration. The ZnO at five different weights was added to the polymeric solution, and the membranes were fabricated by the phase inversion method using water as a nonsolvent and PEG 6 kDa as a pore former additive. The results showed that the pure water flux of the modified membranes increased up to 3 wt% ZnO addition, which was the optimized amount of the nanoparticle addition in this study. Also, at 3 wt% ZnO addition, flux recovery ratio reached from 69% to above 90%, indicated that the nanocomposite membranes were less susceptible to be fouled. BSA rejection of the membranes also enhanced up to 97% by 3 wt% ZnO addition. The membranes were further characterized by SEM images and remarkable changes in their morphologies were observed, and they became more porous with higher interconnectivity between the pores. Furthermore, EDAX analysis was applied to study ZnO dispersion in the membrane structure and except for 4 wt% ZnO addition which particles aggregation was noticeable, ZnO was dispersed finely in the membrane structure. In addition, the modified membranes had higher hydrophilicity and lower contact angle that was effective to obtain higher water flux. (C) 2015 Elsevier B.V. All rights reserved.