The electrical conduction, thermal expansion, chemical reaction, and texture of a sintered body were measured for the mixture of (La, Sr)AlO3 and (La, Sr)(Ga, Mg)O-3, and on the Al-substituted (La, Sr)(Ga, Mg, Al)O-3. No enhancement effect was observed with electrical conductivity by mixing or doping of the Al component. These systems showed lower electrical conductivity than the proportional value of the components. It was considered that the difference of thermal expansion stays at a tolerable level. The grain growth inhibition suggested the strengthening effect of mixing (La, Sr)AlO3, into (La, Sr)(Ga, Mg)O-3. From these results, it is expected that (La, Sr)AlO3 can be used as an electrolyte-protective layer material in order to make a co-fire process possible. In this co-fire, a thin (La, Sr)(Ga, Mg)O-3 electrolyte film will be protected by a very thin (La, Sr)AlO3 film and supported on a Ni-ceramic anode substrate tube or plate. Such a very thin electrolyte will be effective for cost reduction by decreasing the use of Ga.