Crystal structures of Ba-2(In1-xGax)(2)O-5 (n=0.00, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45) were analyzed and electrical conductivity were measured. Rietveld analysis for Ba-2(In1-xGax)(2)O-5 (x = 0.20, 0.25, 0.30, 0.35, 0.40, 0.45) revealed that these oxides are belonging to space group Pm3m (No. 221). This result indicates that the oxide ion vacancies distribute randomly in the cubic perovskite type structure. Fourier transform of In K-edge EXAFS of Ba-2(In1-xGax)(2)O-5 (x = 0.00, 0.10, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45) showed a peak between 1.2 and 2.0 Angstrom attributed to the nearest oxide ions around In3+ cation. The peak was back-Fourier transformed, and the structural parameters were refined by the least-square fitting. The coordination number of In3+ cation increased with increasing Ga3+ cation content. This result indicates that coordination number of Ga3+ cation is 4. Electrical conductivity for pure Ba2In2O5 rapidly increased at about 930 degrees C due to the order-disorder transition of oxygen vacancy. The electrical conductivities of Ba-2(In1-xGax)(2)O-5 (x = 0.25, 0.30, 0.35, 0.40, 0.45) did not show a sharp discontinuity in the conductivity because the disorder phase of defective perovskite type structure was stabilized by doping Ga3+ cations at low temperature. The oxide ion transference number of the Ga-doped Ba2In2O5 was determined by ion blocking method was 1.00. (C) 2000 Elsevier Science B.V. All rights reserved.