The thermodynamic properties of cerium sesquioxide, Ce2O3(s), have been measured. From the low-temperature adiabatic heat capacity measurements in the temperature range 3 K to 420 K, the values for C-p,m(0) and S-m(0), (115.0 +/- 0.3) J . K-1 . mol(-1) and (148.8 +/- 0.4) . J . K-1 . mol(-1), respectively, have been obtained. The high-temperature enthalpy increment has been measured in the temperature range 470 K to 883 K. The enthalpy of solution has been measured by using isoperibol solution calorimetry at T = 298.15 K in 0.250 mol . dm(-3) HCl(aq). Using all available literature values, the standard molar enthalpy of formation has been derived: Delta(f)H(m)(0){Ce2O3(s), 298.15 K} = -(1812.4 +/- 1.3) kJ . mol(-1). The thermodynamic properties have been calculated to T = 1500 K.