The oxygen-ion conductivity of LaGaO 3 electrolytes doped with BaO and MgO is studied. Curved behaviour of the oxygen ion conductivity observed in the Arrhenius plot. Therefore, the activation energy in the low-temperature region is higher than that in the high-temperature region. The dopant cation-oxygen vacancy association, especially the Mg G a '-V . . cluster, may contribute to increase the activation energy in the low-temperature region