Heat capacity of MgSiO3 perovskite has been measured in the temperature range 140--295 K by differential scanning calorimetry. The Kieffer model approach has been used to calculate the heat capacity beyond the measured temperature range. The estimated entropy of MgSiO3 perovskite is 57.2¿1.0 J/mol.K at 298 K which is higher than that of ilmenite, in accord with the negative pressure-temperature slope for the ilmenite-perovskite transition. From the heat capacity thermodynamic Debye temperature of MgSiO3 perovskite is evaluated to be 980¿15 K at 298 K and 1030¿20 K at temperatures above about 700 K. Thermodynamic Gruneisen parameter of MgSiO3 perovskite at 30 GPa and above 1000 K is also estimated as 1.45¿0.15. An adiabatic temperature profile in the pyrolitic lower mantle is calculated with the average gradient of 0.32¿0.04 K/km. The temperature at the top of the D' layer is estimated to be 2500¿100 K. ¿ American Geophysical Union 1993