The biaxial flexural strength and fracture toughness of tape-cast yttria-stabilized zirconia, for application as the electrolyte in solid oxide fuel cells, have been measured at room temperature and at a typical operating temperature of 900 degrees C. The flexural strength was measured in ring-on-ring loading and decreased from 416 MPa at room temperature to 265 MPa at 900 degrees C. The fracture toughness was measured using two different techniques: Indentation fracture and double-torsion loading. The latter was more reliable and gave a fracture toughness of 1.61 +/- 0.12 MPa.m(1/2) at room temperature and 1.02 +/- 0.05 MPa.m(1/2) at 900 degrees C. The flexural strength and fracture toughness were quantitatively consistent with fracture being initiated at the observed surface defects. The lower fracture toughness at 900 degrees C is partly due to a reduction in elastic modulus and partly due to a reduction in the work of fracture.