We found that the partial substitution of Ce for Sr in SrMnO3 could stabilize the perovskite-type structure and made the conductivity increase. In the present study, the structural and electrical properties of Sr0.9Ce0.1MnO3-alpha were investigated by referring to those of Sr0.7Ce0.3MnO3-alpha Sr0.9Ce0.1MnO3-alpha showed the first-order transition from tetragonal to cubic at about 55 degreesC, at which a drastic change in the conductivity occurred. Above this temperature, the conductivity became very high, about 450 S.cm(-1) at 150 degreesC and 270 S.cm(-1) at 800 degreesC. In contrast, Sr0.7Ce0.1MnO3-alpha did not exhibit a drastic phase transition like that in the case of Sr0.9Ce0.1MnO3-alpha. The thermal expansion rate of Sr0.9Ce0.1MnO3-alpha was influenced by the phase transition, but the displacement observed by thermo-mechanical analysis (TMA) was slight at the phase: transition temperature. The chemical compatibility of Sr0.9Ce0.1MnO3-alpha with CeO2-based solid electrolyte was quite good at the fabrication temperature.