Al-substituted a-Ni(OH)2 was synthesized by chemical co-precipitation and its structure and thermal stability were studied through XRD, IR, SEM and TGA. The electrochemical properties were studied by cyclic voltammetric method. The results show that the 25mol% Al-substituted Ni(OH)2 is a-Ni(OH)2 and stable in alkali solution. Compared with )3-Ni(OH)2, the proton diffusion coefficient for a-Ni (OH)2 prepared in this paper is higher and the electrode reaction is controlled by the diffusion.