Tungsten doping to the indium site in Ba2In2O5 was examined, and the electrical properties of the solid solutions were measured using electric and electrochemical methods. The result of X-ray diffraction (XRD) suggested that Ba-2(In1-xWx)(2)O5+3x (x=0.05, 0.10 and 0.15) had cubic perovskite-type lattice at room temperature. The lattice parameter decreased with increasing x, reflecting the small ionic radius of tungsten. The conductivities of the solid solutions increased with doping. They were close to those of the Ba2In2O5-based perovskites. These results supported that the partial substitution of W for In stabilized the high-temperature phase of perovskite-type Ba2In2O5 down to lower temperature. The transport number of oxide ion in W-doped Ba2In2O5 increased with an increase of temperature. On the other hand, the contribution of the proton to conduction decreased with increasing temperature. (C) 2004 Elsevier B.V. All rights reserved.