Porous Nylon-6 membranes with dimethylamino groups were prepared by coagulating the polymer-formic acid solution into water. The effect of LiCl addition in the polymer cast solution on filtration characteristics of the resultant membranes was examined. It was found that resultant membranes have porous structure and show molecular size exclusion property under 0.025-0.1 MPa of applied pressure. Desalination property of the porous membranes was investigated using NaCl solution containing 0.05-0.85 mM concentration. The porous membranes showed effective rejection to saline at lower than 0.2 mM NaCl concentration. (C) 2000 John Wiley & Sons, Inc.