>> In Na-base Battery for ESS, α-Al2O3 and metal bonding was used to prevent direct reaction between electrolyte and electrode. The hard metal was metalized at 1600℃ in a flowing hydrogen gas for high bonding strength. In this study, instead of hard metal metalizing, Ni was plated on α-Al2O3 by electroless Ni plating technique and then bonded with metal. To enhance the bonding strength, surface of α-Al2O3 was treated with H3PO4. The effects of strength and leakage of joining as a function of acid treatment time on α-Al2O3 are described.