In this work, Polyethylenimine (PEI) with different molecular weights was used to alter the surface charge of the aromatic polyamide RO membrane, and the positively charged RO membrane was fabricated by carbodiimide-induced grafting with PEI. The effect of PEI grafting on the surface property (charge, hydrophilicity, chemical elements and morphology) and permselectivity of membrane was analyzed. The results show that the surface charge of resulting membrane was successfully reversed (isoelectric point changed from pH 3.1 to pH 8.0) by the PEI grafting. The membrane surface hydrophilicity was obviously improved as well, which could not only compensate the effect of the increased trans-membrane resistance resulted from the grafted PEI on water flux, but also benefit the anti-fouling property. The morphology of membrane was not obviously affected by the PEI modification. Furthermore, two kinds of representative pollutants, basic protein (lysozyme) and cationic surfactant (DTAC and CTAC) were used as the model pollutant to evaluate membrane anti-fouling property. The PEI-modified membranes show high anti-fouling property to the positively charged pollutants. The novel PEI-modified membrane complements the existing short supply of positively charged RO membranes. (C) 2015 Elsevier B.V. All rights reserved.