A new type of hydrophilic surface modifying macromolecules (LSMMs) were synthesized by end-capping urethane prepolymer with poly(ethylene glycol)s, PEGs, of average molecular weights 400, 600, and 1000 Da and poly(propylene glycol) of a average molecular weight 425 Da. They were characterized and blended into the casting solutions of poly(ether sulfone), PES, to prepare ultra-filtration (UF) membranes by the phase inversion technique. The membranes, both pure PES and LSMM blended PES, were then characterized by contact angle (CA) measurements and UF studies using PEG and poly(ethylene oxide), PEO, solutes of different molecular weights. LSMM blended PES membranes were more hydrophilic than the PES membranes based on CA data. The molecular weight cut-off (MWCO), mean pore size (mu(p)) with geometric standard deviation, pore size distribution, pore density, and surface porosity of the membranes were determined by using UF solutes (PEG and PEO) transport data. LSMMs created lower MWCO, lower mu(p), and also narrower pore size distributions of the PES UF membranes. The significant effect of LSMM blending is discussed. (c) 2006 Elsevier B.V. All rights reserved.