Electrochemical impedance spectroscopy was used to investigate the electrical properties of Ba2In2O5 and the effect of porosity, dopant (Ce), atmosphere, temperature, and grain size on these properties. The effect of dopant was investigated by comparing the results of undoped Ba2In2O5 samples to Ce-doped Ba2In2O5 samples. Effect of grain size for both compositions was studied by comparing the samples made by the glycine-nitrate method, which resulted in smaller grain sizes, and the samples made by the solid-state process, which resulted in larger grain sizes. Porosity effects were determined by testing the samples with different porosities between 20% and 50%. All samples were tested in two different atmospheres, air and 50% H-2/50% N-2, and at different temperatures in the range from 100 degrees C to 500 degrees C. The study contributed to better understanding of the conducting mechanisms of Ba2In2O5 in air and hydrogen-containing atmospheres. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.022202jes] All rights reserved.