Nowadays, gasochromic Pd/WO3 coatings as optically switchable materials during H-2 absorption have become more interesting due to their novel applications in smart windows and gas sensor devices. In this study, WO3 films were fabricated by Pulsed Laser Deposition (PLD) on glass Substrates. Using an electroless method, Pd nanoparticles were deposited on the Surface of the produced films. The effect of Pd growth time on coloring/bleaching rate was studied for different submerging times (1, 2, 5, 10, 15, 20 and 40 min). The best coloring/bleaching velocity was attained with a growth time of 2 min. The effect of growing time and growth feature of Pd particles was further studied using Scanning Electron Microscope (SEM) and X-ray Photoelectron Spectroscopy (XPS). It was revealed that spherical or agglomerate metallic particles have nucleated upon many Surface cracks. The size of particles depends on the growing time and also on the size of cracks, It was observed that hydrogen interaction with a Pd/WO3 layer provides additional surface cracks leading to gasochromic improvement. Furthermore the effect of substrate on Pd growth and gasochromic response was studied. It was observed that the size and distribution of particles as well as gasochromic response depend strongly on WO3 substrate characteristics. (C) 2009 Elsevier B.V. All rights reserved.