The separation performances and physico-chemical characteristics of poly(ether sulfone) membranes were evaluated by blending of surface modifying macromolecules (SMMs). Hydrophobic SMMs (bSMM) and charged SMMs (cSMM) were synthesized and characterized. By addition of SMMs, glass transition temperature decreased and membrane pore size increased. The membrane became more hydrophobic by blending of bSMM, and became more hydrophilic after addition of cSMM. It was also demonstrated by the result of surface free energy study that the bSMM blended membrane showed the lowest solid-liquid (water) interaction by low Lifshitz-van der Waals interaction and Lewis acid (liquid)-base (solid) interaction. In contrast, cSMM blended membrane showed the highest Lewis acid-base interaction, which resulted in the highest interaction energy between membrane surface and liquid (water). It was also found from the result of differential scanning calorimeteric measurement that bound water was formed in the cSMM blended membrane. (C) 2009 Elsevier B.V. All rights reserved.