Peak broadening in X-ray powder diffraction (XRD) profiles of LaNi5-based alloys after hydriding and dehydriding processes, was investigated in order to clarify the relation between the formation of lattice strain and degradation by the hydriding-dehydriding cycling. The degree of peak broadening in XRD profiles was calculated by the Rietveld method and hydrogen capacity was evaluated from P-C isotherms for LaNi5 and LaNi5-alphaMalpha (M: Mn, Fe, Cu, Al; alpha= 0.25, 0.5) after activation and after 1000 hydriding-dehydriding cycles, It was found that an anisotropic peak broadening parameter expressing lattice strain after activation has a linear relation with the decrease in hydrogen capacity. The above parameter is a suitable indicator of the ease of degradation in LaNi5-based alloys. (C) 2000 International Association for Hydrogen Energy.