Nickel hydroxide is widely used as an active material in pasted-type nickel electrodes. Physical properties of several nickel hydroxide powders have been examined by laser diffraction, BET, X-ray diffraction, thermal analysis and SEM. Nickel hydroxide powder with a smaller crystalline size shows better charge-discharge cyclic characteristics. The chemical diffusion coefficients of the proton in the nickel hydroxide sample are measured by a current pulse relaxation method. Nickel hydroxide with a smaller crystalline size shows a higher proton diffusion coefficient, giving excellent cycling behaviour.