In this study, polyethersulfone (PES) nanofiltration membranes were synthesized by blending of O-carboxymethyl chitosan/Fe3O4 nanoparticles via the phase inversion method. O-carboxymethyl chitosan bound Fe3O4 magnetic nanoparticles (CC-Fe(3)O(4)NPs) were synthesized by the binding of carboxymethyl chitosan (CC) onto the surface of Fe3O4 magnetic nanoparticles via co-precipitating method. The modified membranes had considerably higher pure water flux and permeation compared to the unfilled PES membrane. Surface hydrophilicity of the modified membranes was improved due to water affinity improvement of the membrane surface. However, high content of CC-Fe3O4 NPs (>0.5%) in the casting solution diminished membrane performance due to agglomeration of the nanoparticles in the polymer matrix. The antifouling properties of the membranes were evaluated by powder milk solution and measuring the pure water flux recovery ratio (FRR). The 0.5 wt.% CC-Fe3O4 NPs-PES,membrane exhibited the highest FRR value (91.7%) and the lowest irreversible fouling resistance (R-ir) value (8.33%). Nanofiltration performance was also examined by retention of Direct Red 16 dye. As a conclusion, the addition of CC-Fe3O4 NPs at lower concentration could result in membranes with superior pure water flux, higher rejection and good fouling resistance compared to the unfilled PES membrane. (C) 2014 Elsevier B.V. All rights reserved.