A hydrophilic Surface Modifying Macromolecule (LSMM) was synthesized, characterized, and blended into the casting solution of polyethersulfone (PES) membranes. Ultra-filtration membranes were prepared by the phase inversion technique. The membranes were then characterized by contact angle measurements and a solute transport study using poly(ethylene glycol) (PEG) and poly(ethylene oxide) (PEO) solutes of different molecular weights. Pore size and pore size distribution of the membranes were determined by using PEG and PEO separation data. The Ottawa River water was treated by the membranes. The LSMM blended PES membranes showed higher fouling resistance and long-term stability than the PES membrane without LSMM. (C) 2004 Elsevier B.V. All rights reserved.