Heat capacity measurements were performed on zirconia and yttria-doped zirconia, (ZrO2)(1-x)(Y2O3)(x)(x = 0, 0.0200, 0.0396), between 13 and 300 K by adiabatic calorimetry. Powder X-ray diffraction and Raman spectra showed that the structure of the samples with x = 0 and 0.0396 was monoclinic and tetragonal, respectively, while the sample with x = 0.0200 was a mixture of the two phases. The heat capacity of the sample of x = 0.0200 was not estimated on the basis of the additivity rule from the values of the other two samples (x = 0, 0.0396). A broad hump was found around 20 K in the heat capacity curve of CpT-3 versus T of the sample of x = 0.0396.