La0.75Mg0.25Ni3.5-xCo0.2Alx (x=0-0.09) hydrogen storage alloys were prepared by induction melting and effect of Al substitution for Ni on phase constitution and electrochemical property was investigated. With the substitution of A1 for Ni, LaNi5 and LaNi2 phases occurred and (La, Mg)2(Ni, Co, Al)7 phase with hexagonal Ce2Ni7-type structure replaced (La, Mg)2(Ni, C0)7 phase. The cell volumes of LaNi5 and (La,Mg)2(Ni, Co, Al)7 main phases increased with increasing Al content. Some electrochemical properties and kinetic parameters of the alloys,including discharge capacity, high rate discharge ability (HRD), loss angle (ψ), exchange current density (I0) and limiting current density (IL),decreased with increasing amount of substitution of Al for Ni. Substitution of Al for Ni could be favorable for positive shift in corrosion potential of the alloy electrode, and prolonged cyclic lifetime of La0.75Mg0.25Ni3.5_xCo0.2Alx (x=0-0.09) alloy electrodes.