Bilayer Mg/Mn thin films have prepared using thermal evaporation method at pressure 10(-5) torr. Hydrogenation process has been done on pristine and annealed bilayer structure of films at different hydrogen pressure for half an hour. In case of annealed samples partially semiconductor nature is observed and conductivity of films found to decrease with hydrogen pressure and increased with annealing temperature. The XRD analysis shows microcrystalline nature of as-deposited films and after annealing it produce crystalline nature. After hydrogenation an additional peaks of magnesium hydride are also observed that suggesting the presence of hydrogen and hydrogen storage capacity of thin film bilayer structure. Optical band gap of annealed bilayer thin films found to increase with hydrogen pressure. It means hydrogenation process is capable to change bilayer structure from metallic to semi-conducting. The variation in relative resistivity is found nonlinear with time and increases with hydrogen pressure, due to the net effect of hydrogen absorption. Raman spectra show the decrease in intensity of peaks with hydrogen pressure that confirm the presence of hydrogen. Optical photographs are taken in reflection mode that shows a change of color from brown to dark black state with increasing hydrogen gas pressure. This dark black state may be used as solar thermal energy collector because black body is good absorber of heat. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.