Hydrogen purification based on Pd deposition in porous polymeric membranes show promising results for hydrogen permeability and selectivity. It is due to high absorption property of Pd nanoparticles. In this work, gas permeability of carboxylic group functionalized Polyethylene terephthalate (PET) membranes with different time of functionalization have been examined. It has been found that PET membrane having more COOH group shows higher selectivity for Hydrogen (H-2). Further to improve the selectivity, these carboxylated PET membranes dipped in Pd nanoparticles solution for 6 h and found more selective for H2 in comparison to Carbon dioxide (CO2) and Nitrogen (N-2). As the carboxylation increases selectivity of H2 improves drastically in the beginning and nearly get saturated after 24 h. Similar trend has been observed for these membranes after Pd nanoparticles deposition. Fourier transform infrared spectroscopy (FTIR) spectra of these membranes revealed that intensity of peaks related to COOH group at 2968 cm(-1) & 1716 cm(-1) increases with functionalization time. Field Emission Scanning Electron Microscopy (FESEM) was used to study the surface morphology of membranes. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.