It has been shown that strontium beta-alumina is a stable phase at compositions close to SrAl10O17 and can be further stabilized over a composition range in the presence of MgO in the SrO-MgO-Al2O3 system. In the absence of MgO, at temperatures greater than 1673 K, the magnetoplumbite phase is readily formed. Conductivity measurement carried out at temperatures from 1073 to 1773 K has demonstrated that both the strontium beta-alumina and the magnetoplumbite phases have reasonably similar magnitudes of conductivity and activation energy.