Mixed electronic-oxide ionic conductivity in LaGaO3-based oxide doped with Fe, Co or Ni was investigated in this study. The electric conductivity was greatly increased by doping Fe, Co, or Ni for the Ga site of La0.8Sr0.2GaO3. Compared to the conventional mixed electronic-ionic conductors such as LaCoO3, these LaGaO3-based oxides exhibited a lower electronic conductivity but a higher oxide ion conductivity. In particular, Fe-doped LaGaO3 exhibited a high oxygen permeation rate and a stability against reduction. Consequently, higher CH, conversion in the partial oxidation of CH, was attained by using La0.8Sr0.2Ga0.6Fe0.4O3 in the place of the conventional candidate material of La0.6Sr0.4Fe0.8Co0.2O3 for the oxygen permeation membrane. As a result, this study revealed that LaGaO3-based oxide doped with Fe, Co or Ni for Ga site is a new family of mixed electronic-oxide ionic conductors. (C) 2000 Elsevier Science B.V. All rights reserved.