In this study, the functional terpolymer of poly (methyl methacrylate-acrylic acid-vinyl pyrrolidone) was synthesized via free radical solution polymerization using dimethylacetamide (DMAC) as the solvent. The terpolymer can be directly blended with polyethersulfone (PES) using DMAC as the solvent to prepare PES hollow fiber membrane by using a dry-wet spinning technique based on a liquid-liquid phase separation technique. The blended PES hollow fiber membranes showed evident pH sensitivity; and the pH-valve effect was observed at the pH values between 7.0 and 10.0. The fluxes under acid conditions were over 10 times larger than those under basic conditions, and with the increase of the terpolymer blended in the membranes, the flux change increased. The fluxes also showed pH reversibility. Both the pore size change and the electroviscous effect had great effect on the pH sensitivity. Furthermore, the hydrophilicity of the blended membranes increased, and the membranes showed good protein antifouling property. (C) 2010 Elsevier B.V. All rights reserved.