Ultrafiltration membranes with similar pore sizes were prepared from acrylonitrile homopolymer and copolymers with increasing acrylamide content. The membranes containing acrylamide were more hydrophilic, had a smaller dispersion force component of the surface energy, and a smaller negative zeta potential than those prepared from the homopolymer. The effect of the differing surface chemistry of these membranes with similar pore sizes was examined by studying the ultrafiltration of bovine serum albumin (BSA) as a function of feed pH. The hydrophilic membranes showed higher permeate fluxes and flux recoveries than the hydrophobic membrane, in spite of their reduced repulsive electrostatic interaction. With increasing pH, protein transmission increased markedly for the acrylamide containing membranes whereas the transmission through the hydrophobic membrane remained low. These rejection data are explained by the combined effects of the increased hydrophilicity, decreased dispersive surface energy and reduced electrostatic repulsion of the acrylamide containing membranes.