In this paper, functional terpolymers of poly(acrylonitrile-acrylic acid-vinyl pyrrolidone) (P (AN-AA-VP)) with different monomer proportion were synthesized via free radical solution polymerization using N-methyl-2-pyrrolidone (NMP) as the solvent. Fourier transform infrared (FTIR) analysis and differential scanning calorimetry (DSC) confirmed that the terpolymers were successfully synthesized. Elemental analysis data was used to calculate the molar ratio of acrylonitrile (AN), acrylic acid (AA) and vinylpyrrolidone (VP) in the random terpolymers. The molecular weights of the terpolymers were determined by gel permeation chromatography technique (GPC). The terpolymers were water insoluble due to the AN chains. The AA and VP chains were hydrophilic chains. Furthermore, the AA provided negative charge, while the VP provided the miscibility with polyethersulfone (PES), which was widely used as membrane material. Thus, the terpolymers can be directly blended with PES as a macromolecule additive using NMP as the solvent to prepare membranes. The water contact angles for the modified membranes decreased obviously; while the water flux significantly increased, and the membrane flux showed pH dependence; in addition, when the terpolymer was blended in the membrane, the protein adsorption decreased, while the protein anti-fouling property increased. (C) 2009 Elsevier B.V. All rights reserved.