In this paper we develop the mathematical model for the kinetics of isothermal hydriding of metal powders under constant low (near equilibrium) pressures. We consider four successive stages of hydriding: nucleation, skin development, skin growth, and final saturation. Each stage is described by its own equations derived from the mass conservation law. Our approach is to consider a few concurrent processes instead of choosing a single limiting one. We used the model to approximate the series of experimental curves (for successive cycles of hydriding of uranium) and obtained some evaluations for the kinetic parameters. (c) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.