Highly positively charged nanofiltration (NF) membranes have been prepared via a layer-by-layer (LbL) self-assembly technique using graphene oxide (GO) and polyethyleneimine (PEI). The high aspect ratio and unique 2D structure of GO nanosheets enabled them to be easily assembled on the membranesurface, and the intrinsic low resistant channels within the GO nanosheets resulted in a high water flux of the membrane. By assembled a PEI layer on themembrane outer surface, the composite membrane exhibited high positive charge and resulted in the high rejections to multivalent ions. The effects ofdeposition time, PEI and GO concentrations on separation performance of the NF membranes were detailed studied. The best performance among all themembranes was achieved with salt rejections of 93.9% and 38.1% for Mg2+ and Na+, and a water flux of 4.2 L/m(2) h bar at 30 degrees C and 0.5 MPa. Theattractive performance of these NF membranes showed a great potential in the industrial application of water softening. (C) 2016 Elsevier B.V. All rights reserved.