The PuNi 3 -type intermetallic compounds LaNi 3 , CaNi 3 , La 0 . 5 Ca 0 . 5 Ni 3 , LaCaMgNi 9 , La 0 . 5 Ca 1 . 5 MgNi 9 , CaTiMgNi 9 , LaCaMgNi 6 Al 3 and LaCaMgNi 6 Mn 3 have been prepared using a powder-metallurgy-sintering method. The hydrogenation behaviour of these materials has been studied through the gas-solid reaction. The as-prepared compounds were easily activated at room temperature under a hydrogen pressure of 3.3 MPa. The pressure-composition-temperature (P-C-T) curves show a single plateau region with the exception of LaNi 3 -H, which shows no plateau, and La 0 . 5 Ca 1 . 5 MgNi 9 -H, which shows two plateaus. All of these alloys can absorb/desorb hydrogen by 1.8 wt.% under the conditions studied. X-ray diffraction (XRD) analysis reveals that LaNi 3 H 4 . 5 is in the amorphous state, and the other hydrides are accompanied by different expansions of the unit cell volume of the host alloy.