Polymer blend membranes of polysulphone (PSF) and polycarbonate (PC) in different concentration ratios (9:1, 3:1 and 1:1) were prepared by a solution cast method. FeCl3 doped polycarbonate membranes in different concentrations ratios (10, 20 and 30) were also prepared using the same technique. The gas permeability of H-2 and CO2 has been observed for these samples. The doped membranes were etched in 6N NaOH at 60(+/- 2) degrees C by step etching and the permeability was observed for every step. It was observed that the permeability of the membranes was increased with an increase in etching time. The rapid variation in permeability was found after a critical etching time. The formation of C-Fe bonds in the polymer may be improving its stability against the etchant. In the blend membrane, it was observed that as the concentration of PC in PSF increases the permeability of both the gases (H-2 and CO2) increases. The permselectivity of hydrogen over carbon dioxide was calculated to be 2.52 for pure PSF and it reduces as the concentration of PC in PSF increases. The optical micrograph shows complete dispersion of FeCl3 in PC and XRF confirms the elemental composition. (C) 2007 International Association for Hydrogen Energy.