A novel ultrafiltration (UF) membrane with controllable selectivity for protein separation was obtained by altering the structure of the thick sieving layer on the membrane surface and subsurface. Poly(vinyl pyrrolidone) (PVP) was first cross-linked on/in the poly(vinylidene fluoride) (PVDF) hollow fiber microfiltration (MF) membrane to attract more sulfobetaine (SB) monomer adjacent to membrane for subsequent grafting polymerization and the formed thick sulfobetaine polymer (PSB) layer on the membrane surface and subsurface acted as the sieving layer with environment sensitivity. After immersed in 20 mmol/L NaCI solution at 60 degrees C, the novel UF membrane with the sieving layer of 4.8 mu m showed high permeate capacity with a water flux of 590 L/m(2) h and a good selective behavior with MWCO of 95-110 kDa. The protein mixture (BSA and Lys) could be separated through the novel UF membrane efficiently by isoelectric focusing of one component with a larger size (BSA). By means of the simple immersion in pure water, the membrane permeated most of proteins and the degree of flux decline reduced obviously. After swelled in NaCI solution again, the membrane restored the selectivity and the protein separation efficiency. Such novel smart UF membrane is an attractive candidate for the batch separation of protein mixtures, expanding the membrane application in the fields of agro-food, biomedicine and other bio-filtration. (C) 2012 Elsevier B.V. All rights reserved.