We synthesized BaIn1-xCoxO3-delta (x=0-0.8) with a defective perovskite structure by partly replacing In with Co in Ba2In2O5. Based on XRD measurements, the synthesized compound was found to have cubic perovskite and orthorhombic brownmillerite structures depending on the amount of Co. BaIn1-xCoxO3-delta (x=0.2 and 0.3) showed high total electrical conductivities without undergoing the structural transformation that the original Ba2In2O5 undergoes. Some of the samples showed both electronic and oxide ionic conductivities. At the same time, the oxide ionic conductivity was comparable with that of Ba2In2O5. For example, the sample with x=0.1 had a total electrical conductivity of 4.7 x 10(-1) S cm(-1) and an oxide ion transport number of 0.52 at 850 degrees C. (c) 2006 Elsevier B.V. All rights reserved.