A particulate positive electrode active material for an alkaline storage battery comprising: (a) solid solution nickel hydroxide particles containing at least magnesium and (b) a coating layer comprising cobalt oxide being formed on the surface of the solid solution nickel hydroxide particles. The amount of magnesium contained in the solid solution nickel hydroxide particles (a) is not smaller than 2 mol % and not larger than 15 mol % of the total amount of metal elements contained in the solid solution nickel hydroxide particles (a). BET specific surface area of the solid solution nickel hydroxide particles (a) measured by nitrogen gas adsorption is not smaller than 5 m.sup.2/g and not larger than 15 m.sup.2/g. The coating layer (b) further comprises at least one element Xs selected from the group consisting of yttrium, ytterbium, lutetium, titanium and calcium.