The present invention relates to an alkaline secondary battery improved in the structure of the plate substrate, and provides an alkaline secondary battery which uses a three-dimensional porous substrate which is inexpensive, improved in stability in electrolyte and inhibited from shrinkage at sintering. The battery has such a construction comprising a sealed case containing positive electrodes mainly composed of a nickel oxide, negative electrodes mainly composed of a hydrogen-absorbing alloy or a cadmium oxide, an alkaline electrolyte containing at least one component selected from the group consisting of potassium hydroxide, lithium hydroxide and sodium hydroxide and separators, the substrate used for at least one of the positive electrode and the negative electrode being a three-dimensional porous iron sintered body on the surface of which is provided a nickel coating layer.