The fracture strength, fracture toughness, and electrical conductivity of less than 7 mol% Sc2O3-doped zirconia polycrystals consisting of submicron grains were investigated, which were fabricated from fine powders prepared by the homogeneous precipitation method using zirconia sols previously formed by the thermal hydrolysis of ZrOCl2 solution. An electrical conductivity of 0.09 S/cm at 1000 degrees C was observed in 4 mol% Sc2O3-doped zirconia having a uniform microstructure (grain size < 0.4 mu m) and consisting of a fully tetragonal phase-this value corresponds to nearly twice that of 3 mol % Y2O3-doped tetragonal zirconia, and the activation energy of the ionic conductivity was 0.82 eV (800 similar to 1000 degrees C). The average bending strength for 4 mol % Sc2O3-doped tetragonal zirconia was 640 MPa, and its fracture toughness was 3.9 MPa . m(1/2). The present Sc2O3-doped tetragonal zirconia ceramics with high electrical conductivity and high fracture strength have another possibility as a candidate electrolyte material for planar type solid oxide fuel cells.