In this study, SnO2 and ZnO were co-doped in In2O3, and the phase development and electrical characteristics were examined. When Zn2+ was added to 20 at.% Sn4+ contained In2O3, in which a large amount of In4Sn3O12 second phase exists, the amount of the second phase decreased as the content of Zn2+ increased, which promoted grain growth and increased carrier mobility. In the case of a simultaneous substitution of Sn4+ and Zn2+ into In2O3 with almost the same atomic ratio, a large grain size without second phase was observed, while small grain sizes with many second phases were developed when Sn4+ and Zn2+ were added with different atomic ratios. The electrical characteristics analyzed by Hall effect measurement showed that the electron mobility and conductivity showed a close relationship with the microstructure, while the carrier concentration was almost constant regardless of the Zn2+ content. (c) 2006 Elsevier B.V. All rights reserved.