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.