The 25 pm thick polymer blends of PSF and PC were prepared in different concentrations viz. (3: 1), (1: 1) and (0: 1), by solution cast method. These membranes were then irradiated by Ni7+ heavy ion of 100MeV at Inter University Accelerator Centre, New Delhi, India. The gas permeability for hydrogen and carbon dioxide of these membranes was measured as a function of etching time. The permeability was found to be increasing with the increase in PC concentration in blends. The permeability of irradiated membranes was measured from both the sides. It was observed that the permeability for the front side was larger than that for the backside, which shows asymmetric behavior of membranes. Besides these, permeability was also found to depend upon fluence of ions. Permeability of membranes irradiated by high fluence of ions was higher than the membrane irradiated with the low fluence of ions. (c) 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.