Abstract: The crystal structure of LaNi₅ alloy after longterm storage of tritium was investigated by means of X-ray diffraction (XRD). The results show broadened peaks on the XRD spectra of the specimens compared with that of the as-received ones, indicating clear aging effects of the alloy. The main reason causing the aging effects of the alloy is likely due to the tritium produced ³He, which might induce dislocation sub-structures in the crystal. The alloy shows the ability to be near fully recovered through high temperature treatment.