Effects of substitution with foreign metals on the crystallographic, thermodynamic and electrochemical properties of AB(5)-type hydrogen storage alloys were investigated. The unit cell volume of MmNi(5-x)Al(x) (Mm = mischmetal, 0.2 less than or equal to x less than or equal to 1.0) alloys and the values of enthalpy change (-Delta H) in hydride formation increased monotonously with an increase in x-value, but the discharge capacity and high-rate dischargeability had a limiting value. For the MmNi(4.2)Al(0.4)M(0.4) (M = Cr, Mn, Fe, Co) alloys, both the unit cell volume and the -Delta H value increased with increasing metallic bond radius of the foreign metal. Especially, manganese improved the discharge capacity and the high-rate dischargeability.