PURPOSE: To prevent electrode swelling by adding a small amount of Co to a Ni hydroxide powder as a Ni electrode active mass of an alkaline secondary battery.

CONSTITUTION: In Ni(OH)2 powder as a Ni electrode active mass for an alkaline secondary battery, the inside of the powder is Ni(OH)2 single composition. Meanwhile the surface part has a bilayer structure comprised of Ni(OH)2 and a solid solution composition with Co(OH)2, (Ni, Co)(OH)2. The content of the Co(OH)2 is ≥20wt.%. In this way, a Ni electrode active mass having resistance to swelling is obtained.