Poly(acrylonitrile) (PAN)-based zwitterionic membranes were fabricated through phase inversion in a wet process. It was found that bovine serum albumin (BSA) can adsorb on PAN-based zwitterionic membranes in the absent of electrolyte. A new viewpoint based on electrostatic interactions between the charged amino acid residues in BSA and dipole moments of sulfobetaine groups in the zwitterionic polymers in the absent of salt was put forward to explain the adsorption of protein on the zwitterionic membranes. The adsorbed BSA on PAN-based zwitterionic membranes can be released fast and completely from the membranes at higher NaCl concentration. The controlled adsorption and desorption of BSA on PAN-based zwitterionic membranes was achieved through adjusting NaCl concentration in solution. (C) 2007 Elsevier Ltd. All rights reserved.