A process for purifying aqueous solutions containing macromolecular proteins such as bovine serum albumin (BSA), egg albumin (EA), pepsin, and trypsin has been investigated. Protein removal from food and biorelated industrial waste streams are gaining increased visibility due to environmental concern and saving precious materials. Ultrafiltration (UF) processes are largely being applied for protein separation from aqueous streams. In this work, an attempt has been made to separate the valuable proteins using cellulose acetate (CA)/sulfonated poly(ether imide) (SPEI) blend UF membranes prepared in the absence and presence of the additive, polyethyleneglycol (PEG600) in various compositions. The blend membranes were subjected to the determination of pore statistics and molecular weight cut-off (MWCO). Porosity and pore size of the membranes increased with increasing concentrations of SPEI and PEG600 in the casting solution. Similarly, the MWCOs of the blend membranes ranged from 20 to greater than 69 kDa, depending on the Various polymer blend compositions. Surface morphology of the blend membranes were analyzed using scanning electron microscopy. Studies were carried out to find the rejection and permeate flux of proteins. 011 increasing the concentration of SPEI and PEG600, the rejection of proteins is decreasing, whereas the permeate flux has an increasing trend. The effect of hydrophilicity of SPET on fouling of protein for CA/SPEI blend membranes was also discussed. (c) 2008 Wiley Periodicals, Inc.