The bending strength of alumina-toughened 8 mol% yttria fully stabilized zirconia was examined after high temperature annealing. When the specimens were annealed at 1000 or 800 degrees C, their bending strengths initially retained their starting value, decreased and then levelled off. The toughening mechanisms and the ionic conductivity of the composite were investigated to confirm the suitability of the composite as electrolyte of solid oxide fuel cells.