Mg2Ni-type Mg2-xLaxNi (x=0, 0.2, 0.4, 0.6) hydrogen storage alloys were prepared by casting and rapid quenching, respectively. The microstructures of the as-cast and quenched alloys were studied by XRD, SEM and HRTEM. Results show that no amorphous phase forms in the as-quenched La-free alloy, but the as-quenched alloys containing La hold a major amorphous phase. Thermal stability of the as-quenched alloys was studied by DSC, and the results show that La content and the quenching rate induce a negligible influence on the crystallization temperature of the amorphous phase. The electrochemical measurement shows that the discharge capacity of the as-cast alloys grows with the increase of La content, while the as-quenched alloys obtain the maximum discharge capacities with the variation of La content. The substitution of La for Mg markedly enhances the cycle stability of the as-cast and quenched alloys