In this work, the influence of microstructure on the hydrogen permeation property of alumina coatings was investigated. The different microstructures were obtained by annealing coatings at 700 degrees C or 900 degrees C. The permeation measurements showed that the 700 degrees C annealed coating exhibited lower hydrogen permeability than the 900 degrees C annealed coating. The 700 degrees C annealed coating was amorphous alumina. While, the 900 degrees C annealed coating had the spinel MnCr2O4 phase and gamma-alumina. This spinel MnCr2O4 formed a network on the coating surface compared with the fine and smooth surface of the 700 degrees C annealed coating. The MnCr2O4 network in the 900 degrees C annealed coating formed short-cut for hydrogen diffusion, and thus resulted in high permeability. Furthermore, apparent delamination of coating was illustrated on the 900 degrees C annealed coating after the permeation test, and this was another reason for the high permeability of coating. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.