Abstract Porous and dense ZrO2–4mol.% Y2O3 ceramics were fabricated by spark plasma sintering at 1100 and 1500°C. The porosity of the ceramics sintered at 1100°C increased with the addition of ∼0–5mol.% Gd2O3. In contrast, the ceramics sintered at 1500°C showed full density regardless of the amount of Gd2O3 addition. The fluorite-type Gd2Zr2O7 phase was formed as the second phase in the tetragonal ZrO2 matrix. The thermal diffusivity and thermal conductivity of sintered ZrO2–4mol.% Y2O3 decreased with increasing Gd2O3 addition.