Storage capacity and fast reaction rate are the most important properties for hydrogen storage alloys. To clarify the mechanism of the rate-controlling step, we analyzed the hydrogen diffusion coefficients of the hydride by the homogenization method, which considers the microstructure of the alloy at the microscale (0.1-10 mum) precisely. By applying nucleation and growth model, we have discussed the absorbing and desorbing mechanism of the metal hydride. Our results and analysis show that it is important for the hydriding or dehydriding reaction to consider the number of nuclei and the transfer of hydrogen atom through the alpha-beta interface data. Estimation of the microstructure of the metal hydride by using the homogenization method is useful for the absorbing and desorbing mechanism. (C) 2002 International Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved.