The effects of substitution of Ce for La on the microstructure and electrochemical performance of LaCeMgNiCoAl (x = 0, 0.05, 0.1, 0.2, 0.3, 0.4) hydrogen storage alloys were investigated. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) analyses showed that the main phases of the alloys consist of (La, Mg)Ni phase (PuNi-type rhombohedral structure), LaNi phase (CaCu-type hexagonal structure) and (La, Mg)Ni phase (CeNi-type hexagonal structure). The cell volume of the (La, Mg)Ni phase, (La, Mg)Ni phase and LaNi phase decreased monotonously with increasing Ce content. Electrochemical investigations showed a decrease in the discharge capacity, while high rate dischargeability (HRD) first increased and then decreased with increasing Ce content. The Ce substitution for La slightly enhanced the cyclic stability of the alloy electrodes. The pressure-composition (P-C) isotherms showed that the plateau region was broadened with Ce content increased in the alloys, meanwhile, two plateaus appeared and pressure of the hydrogen absorption and desorption increased accordingly. © 2009 Professor T. Nejat Veziroglu.