Thermodynamic properties were studied by molecular dynamics simulation far the samples of 8, 10, 12 and 14 mol% Y2O3 doped ZrO2. The phonon density of states and the heat capacity were calculated. The calculation showed extra vibrational modes at low frequencies caused by structural defects in the crystal, and confirmed the excess heat capacity around 25 K which had been previously detected by heat capacity measurements. The composition dependence of the excess heat capacity showed a maximum at 10 mol%, which coincided with the experimental results.