Ionic conductivities of Ni/Al layered double hydroxides (Ni–Al LDHs) intercalated with CO 3 2 - , Cl− and OH− were evaluated in the temperature range of 25–80°C under 65–95% relative humidity. X-ray diffraction and Fourier transform infrared measurements confirmed the formation of Ni–Al LDHs intercalated with CO 3 2 - , Cl− and OH−. In the AC conductivity measurements, Ni–Al LDH intercalated with CO 3 2 - (Ni–Al CO 3 2 - LDH) showed the highest ionic conductivity among them. The ionic conductivity of Ni–Al CO 3 2 - LDH was 1.3×10−2 Scm−1 at 80°C under 80% relative humidity. The electromotive force for the water vapor concentration cell using Ni–Al CO 3 2 - LDH showed similar behavior with that using anion exchange membrane, indicating that Ni–Al CO 3 2 - LDH is a hydroxide ion conductor. Pelletized Ni–Al CO 3 2 - LDH was confirmed to work as the electrolyte of alkaline-type direct ethanol fuel cell.