This study reports on the surface modification of ultrafiltration membranes using the layer-by-layer (LbL) technique. The novelty of this work resides in the LbL assembly of charged polyelectrolytes by electrostatic adsorption directly onto the ultrafiltration membranes without any prior treatment of the surface. Polyethersulfone ultrafiltration membranes have been employed for the deposition of branched poly(ethyleneimine) and poly(sodium 4-styrene sulfonate) to create a thin polyelectrolyte film on their surface. The modified membranes are characterized by their permeability and molecular weight cut-off (MWCO) value. Experiments show that the deposited polyelectrolyte layer causes a decrease in the permeability due to the additional resistance of the layers. However, the MWCO value is shifted meaning a better rejection of the dextran solution is achieved. Thus, the LbL assembly of polyelectrolyte multilayers on the surface of the membrane makes it possible to convert a membrane with open structure to a membrane with denser active layer. (C) 2009 Elsevier B.V. All rights reserved.