To reduce membrane fouling of reverse osmosis (RO) membrane, we adopted layer-by-layer (LbL) assembly. LbL assembly has received attention as a means of preparing ultrathin layers of composite membranes. In addition, it can suppress membrane fouling due to its hydrophilicity. In this study, we deposited polyelectrolytes on a commercial RO membrane via LbL assembly and especially investigated the effect of layer number on membrane properties. The obtained membranes exhibited antifouling properties, such as high water permeability and high ion rejection, against various hydrophobic foulants. In addition, membrane hydrophilicity increased and surface roughness became smooth as layer number increased. We also found an optimum layer number that admitted highest water permeability. Quartz crystal microbalance with dissipation measurements revealed that the polyelectrolyte multilayer indeed suppresses foulant adsorption. Protein conformational change was low on the polyelectrolyte film surface, compared with that on the polyamide layer. (C) 2012 Elsevier B.V. All rights reserved.