Abstract: EMF of the concentration cells of sodium beta alumina tubes in four aqueous solutions: NaOH, NaOH-KOH, NaOH-(CH_3)_4NOH and NaOH-NaCl were measured. The potential differences across the Na-beta alumina/NaOH aqueous solution interfaces Δφ, were obtained. The results showed that the relations between Δφ and loga_2 (Na)~+/a_1(Na~+) obeyed the Nernst equation in NaOH, NaOH-NaCl aqueous solutions. The presence of K~+ ions influenced Δφ, but OH~-, (CH_3)_4N~+ did not. The possi- bility of using the beta alumina as a Na~+-ion selective electrode in alkaline Na~+-ion aqueous solutions (if Na~+ concentration≥0.01 mol L~(-1).) was discussed.