Mg is a promising light-weight material that has superior hydrogen storage capacity. However H-2 storage in Mg typically requires high temperature, similar to 500-600 K. Furthermore it has been shown that there is a peculiar film thickness effect on H-2 sorption in Mg films, that is thinner Mg films desorb H-2 at higher temperature [1]. In this study we show that the morphology of DC magnetron sputtered Mg thin films on rigid SiO2 substrate varied from a continuous dense morphology to porous columnar structure when they grew thicker. Sputtered Mg films absorbed H-2 at 373 K and evolved into a metastable orthorhombic Mg hydride phase. Thermal desorption spectroscopy studies show that thinner dense MgH2 films desorb H-2 at lower temperature than thicker porous MgH2 films. Meanwhile MgH2 pillars with greater porosity have degraded hydrogen sorption performance contradictory to general wisdom. The influences of stress on formation of metastable MgH2 phase and consequent reduction of H-2 sorption temperature are discussed. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.