Dissolution enthalpies of Sm2O3, BaCO3, CuO, SmBa2Cu3O6.92, BaCuO2 at 323.15 K in 2N HCl were measured by solution calorimetry. On the basis of these data, the enthalpies of the following reactions were obtained: (1) 0.5Sm(2)O(3) + 2BaCO(3) + 3CuO + 0.21O(2) - SmBa2Cu3O6.92 + 2CO(2); (2) 0.5Sm(2)O(3) + 2BaO + 3CuO + 0.21O(2) = SmBa2Cu3O6.92; (3) 0.5Sm(2)O(3) + 2BaCuO(2) + CuO + 0.21O(2) = SmBa2Cu3O6.92. It was established that SmBa2Cu3O6.92 was thermodynamically unstable with respect to the interaction with CO2 and thermodynamically stable with respect to the mixture including BaCuO2. The standard formation enthalpy of SmBa2Cu3O6.92 was calculated as following: Delta(f)Hdegrees (SmBa2Cu3O6.9, s, 323.15 K) = -2672.30 +/-5.01 kJ/mol.