Significant improvement in the fracture strength, accompanied by an enhancement in the electrical conductivity, of zirconia polycrystals that were doped with 3-7 mol% Sc2O3 was obtained by sintering at 1300 degrees C for 1 h in air, followed by hot isostatic pressing (HIP) at 196 MPa at 1300 degrees and 1450 degrees C for 1.5 h in an argon-gas atmosphere. Dense bodies (with an average grain size of <0.5 mu m) that were doped with 3.5 mol% of Sc2O3 showed the highest average fracture strength up to 1770 MPa and an electrical conductivity of 0.08 S/cm at 1000 degrees C. The present zirconia ceramics, which consisted of submicrometer-sized grains of tetragonal phases and were stabilized with 5 and 6 mol% of Sc2O3, exhibited high strength (1330 and 1140 MPa, respectively) and good conductivity (0.15 and 0.18 S/cm, respectively); values for both properties were greater than those previously reported. The present HIPed zirconia ceramics, which have excellent properties, are candidates for an electrolyte of planar-type solid oxide fuel cells.