The phase diagrams of pseudo-binary systems LaNi5-NdNi5 and LaNi5-CeNi5, the aniso-tropy of grain sizes of actived LaNi5-NdNi5 samples, hydrogen absorption capacity and hydrogen desorption isotherms at 29℃ and influence of other phase on hydrogen absorption characteristics of LaNi5 have been investigated by means of X-ray diffraction and DTA, X-ray diffraction line broadening method, and second ways respectively.The variations of lattice parameters, unit cell volumes and atomic distances of actived and unactived samples were determined.The anisotropy of grain sizes of actived LaNi5-NdNi5 system, the difference of hydrogen absorption capacity and hydrogen absorption plateau pressures of RmNi5(Rm = misch-metal) were explained from structure viewpoint and our experimental results.