Acid functionalized multi-walled carbon nanotube (MWCNT) was modified by three hydrophilic polymers during an in situ polymerization reaction. Citric acid (CA), acrylic acid (AA) and acrylamide (AAm) were polymerized on functionalized MWCNTs to achieve greater number of functional groups on MWCNTs. Fourier transform infrared spectroscopy (FTIR) validated the formation of hydroxyl, carboxyl and amide groups on MWCNTs. Mixed matrix membranes were prepared by introducing 0.1 wt% of acid functionalized and polymer modified MWCNTs into polyethersulfone (PES) membranes. Water permeability and antifouling capability of prepared membranes were compared. According to the results, mixed matrix membranes showed higher pure water flux compared to pristine PES membrane. Hydrophilicity of polymer modified MWCNT/PES nanocomposite membrane was improved for all three polymers. The results indicated that hyperbranched polycitricacid (PCA) on MWCNTs offered large number of functional groups and significantly improved membrane fouling resistance against whey proteins. Efficient dispersion of PCA modified MWCNT in casting solution led to smooth and hydrophilic membrane surface and consequently higher flux recovery ratio (95%). Existence of PCA dendrimers on MWCNT increased the carbon nanotubes compatibility with membrane bulk polymer and resulted in superior dispersion of nanofiller in membrane matrix and its surface. The morphology and surface characteristics of prepared membrane were investigated by field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM) and water contact angle (WCA) measurement. (C) 2013 Elsevier B.V. All rights reserved.