Sintered pellets of Ce-doped Ba2In2O5 (BIC) were prepared from nanopowders. The electrical conductivities were measured using ac impedance spectroscopy under different atmospheres and temperatures. The electrical conductivity of sintered BIC was found sensitive to environmental humidity when the temperature was below 300 degrees C. However, in the presence of hydrogen, the electrical conductivities were independent of water content in the range of 0-30 vol%. The electrical conductivities of BIC were significantly affected by the presence of hydrogen in a temperature range of 100-300 degrees C. The estimated protonic transference number and the measured open circuit voltage suggested the existence of electronic conduction. The coefficient of thermal expansion of BIC is 11.2 x 10(-6) K-1 from 25 to 1250 degrees C. (c) 2006 Elsevier B.V. All rights reserved.