The phase structure and electrochemical properties of La 2 Mg 1-x Al x Ni 7.5 Co 1.5 (x=0.0,0.1,0.3,0.5) alloys were investigated by means of X-ray diffraction (XRD), electron probe X-Ray microanalysis (EPMA) and electrochemical measurements. XRD and EPMA results show that small quantity replacement Mg by Al (x=0.1) does not change phase composition of La 2 MgNi 7.5 Co 1.5 alloy, the alloy is still constituted with LaNi 3 phase and Ξ±La 2 Ni 7 phase, but the abundance of LaNi 3 phase decreases obviously and that of Ξ±La 2 Ni 7 increases in the La 2 Mg 0.9 Al 0.1 Ni 7.5 Co 1.5 alloy. The more Al substitution will change phase composition of the alloy, resulting in LaNi 3 phase disappearance. Influence of change of Al content on cell parameters of different phases of the La 2 Mg 1-x Al x Ni 7.5 Co 1.5 alloy is different. Moreover, little replacement of Mg by Al (x=0.1) lowers scarcely hydrogen storage capacity and maximum electrochemical discharge capacity of the alloy, but with the increment of Al content in the La 2 Mg 1-x Mg x Ni 7.5 Co 1.5 alloy, hydrogen storage capacity, activation property and maximum electrochemical discharge capacity of the alloys decrease continuously. Al substitution for Mg can improve obviously electrochemical cyclic stability of La 2 MgNi 7.5 Co 1.5 alloy electrode, and is beneficial to improve high rate dischargeability of the alloy electrode.