As an electrolyte material for reduced temperature solid oxide fuel cell (SOFC), La1-xSrxScO3 - (alpha) (x = 0.05 -0.5) solid oxides with high ionic conductivity were synthesized by the solid phase method. The electrical conductivity rose as the value of x increased. For x greater than or equal to 0.35, the compound underwent a phase transition at 1073K. Adding 2 mol% Al to the Sc site was very effective in suppressing this transition. However, the electrical conductivity of La0.65Sr0.35Sc0.98Al0.02O3 was lower than that of La0.675Sr0.325ScO3. La0.675Sr0.325ScO3, an unstable solid, maintained high ionic conductivity even when effectively stabilized by 1 mol% Al doping at the Sc site. Furthermore, no n-type conduction of La0.675Sr0.325Sc0.99Al0.01O3 was observed under low oxygen partial pressure. (C) 2003 Elsevier Science B.V. All rights reserved.