Thermal property characterization of a metal hydride was conducted in a high pressure hydrogen environment with a transient plane source apparatus. This apparatus was integrated with a pressure vessel to measure the effective thermal conductivity and the thermal diffusivity of non-reactive and activated metal hydrides in hydrogen pressures up to 275 bar and 253 bar, respectively. In a non-reactive oxidized condition, the effective thermal conductivity of Ti(1.1)CrMn powder increased with hydrogen pressure from 0.8 to 1.6 W/m.K. For activated powder, effective thermal conductivity increased from 0.3 to 0.7 W/m.K with hydrogen pressure. It is postulated that the smaller particle size associated with the reactive condition caused the reduction in effective thermal conductivity. Also, the derived specific heat of the activated Ti(1.1)CrMn increased with reaction progress by a factor of two, with a maximum value at the fully hydrided state. (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.