The heat capacity of 9.70 and 11.35 mol% yttria stabilized zirconia ((ZrO2)1–x(Y2O3)x; x=0.0970, 0.1135) was measured by adiabatic calorimetry between 13 and 300 K, and some thermodynamic functions were calculated and given in a table. A large excess heat capacity extending from the lowest temperature to room temperature with a broad maximum at about 75 K was found in comparison with the heat capacity calculated from those of pure zirconia and yttria on the basis of simple additivity rule. The shape of the excess heat capacity is very similar to the Schottky anomaly, which may be attributed to a softening of lattice vibration. The amount of the excess heat capacity decreased with increasing yttria doping, while the maximum temperature did not vary. The relationships among the excess heat capacity, defect structure and interatomic force constants, and also the role of oxygen vacancy were discussed.