In this article, multi-component protein fractionation was studied by mosaic membrane partitioned free-flow isoelectric focusing (FFIEF). The mosaic membranes were molecularly designed through a blending of aminated poly(2,6-dimethy1-1,4-phenylene oxide) (APPO) and sulfonated polysulfone (SPSf) with polysulfone (PSf). All cast membranes were prepared from the same dope but phase inverted in different coagulants to produce different morphologies. Membrane characterizations through field emission scanning electron microscopy (FESEM) imaging, streaming potential, pore size distribution and PWP (pure water permeation) demonstrated that the self-prepared membranes possessed a variety of membrane structures and charge characteristics. These mosaic membranes were applied in FFIEF as the selective barriers. Experimental results show that a blend of APPO and SPSf with PSf is an effective route to produce highly charged mosaic membranes, which can be used in the separation of five pure protein components from chicken egg white using the mosaic-membrane partitioned FFIEF. (C) 2010 Elsevier B.V. All rights reserved.