The streaming potential was measured across polyethersulfone and sulfonated polysulfone ultrafiltration membranes in order to estimate an apparent zeta potential. The influence of bovine serum albumin adsorption on this potential was studied, and the results showed that most of the pore walls after adsorption had a surface property behavior very similar to that of the protein. Hence, at low ionic strength, protein-fouled membrane interactions were repulsive in nature. This repulsion contributed to the partial exclusion of proteins from the membrane porous structure, and thus reduced the protein transmission, which was experimentally studied by diffusion.