Toward understanding physical interaction of hydrogen isotopes with alpha-Al2O3 barrier, adsorption, dissociation and diffusion of hydrogen in alpha-Al2O3(0001) slab have been investigated by density functional theory (OFT) and rate theory. H-2 molecule, with parallel configuration, preferentially absorbs on a top Al atom site of first atomic layer on alpha-Al2O3(0001) surface, while H atom strongly bonds at a top O atom site of the second atomic layer, H atoms recombine into molecules on top Al atom sites of the third atomic layer. The barrier for H-2 exothermic dissociation on surface is 0.79 eV. The potential energy pathways of H diffusion in alpha-Al2O3 are studied, predicting that H atom diffusion preferentially occurs via surface path rather than bulk path involving elementary reorientation and hopping steps. The surface-to-subsurface diffusion is significantly endothermic except for the surface and subsurface-to-bulk path. Mechanism, in well agreement with experimental result, of alpha-Al2O3 a resisting hydrogen permeation has proposed. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.