Nanoporous polyacrylonitrile (PAN) membranes were prepared by a supercritical carbon dioxide induced phase separation method from a solution containing dimethyl formamide as the solvent. The influence of the experiment parameters, including temperatures, pressures and polymer concentrations, on the morphology of the nanoporous membrane were investigated in detail. The porosities of the obtained membranes were characterized by scanning electron microscopy and nitrogen adsorption technique. The PAN membranes demonstrate high pure water flux and high size selectivity, which have promising applications for the nanofiltration. (C) 2016 Elsevier B.V. All rights reserved.