A weak polyelectrolyte ultrafiltration membrane based on poly(acrylonitrile and 2-dimethylamino ethyl methacrylate) (PAN-DMAEMA) copolymer was prepared by phase inversion in a wet process. PAN-DMAEMA membrane has the typical asymmetric structure. The results of X-ray photoelectron spectroscopy (XPS) analysis have shown enrichment of PDMAEMA on the membrane surface. Water flux of PAN-DMAEMA ultrafiltration membrane is tunable due to the switch of the stretched and collapsed states of PDMAEMA chains at different pH and NaCl concentration in the feed solutions. The water flux of PAN-DMAEMA membrane cannot reversibly recover its original flux after environmental stimuli; the reason may be that the residual exchanged-ions and ionic pairs disturb the switch of polymer conformation of PDMAEMA in the skin layer of ultrafiltration membrane. (c) 2007 Elsevier B.V. All rights reserved.