The preparation of BaCeO3 doped by gadolinium, europium, and terbium oxides (BaCe0.8Eu0.1Tb0.1O2.9 and BaCe0.8Gd0.2O2.9) has been performed by solid-state reaction from BaCO3, CeO2, Gd2O3, Eu2O3, Tb4O7. The X-ray measurements have showed that BaCe0.8RE0.2O2.9 (RE = Gd, Eu, Tb) was orthorhombic structure (space group Pnma). The standard formation enthalpies of BaCe0.8Eu0.1Tb0.1O2.9 and BaCe0.8Gd0.2O2.9 have been determined by solution calorimetry combining the solution enthalpies of BaCeo.8GdO.202.9 (BaCe0.8Eu0.1Tb0.1O2.9) and BaCl2 + 0.8CeCl(3) + 0.2GdCl(3) (BaCl2 + 0.8CeCl(3) + 0.1EuCl(3) + 0.1TbCl(3)) mixtures in 1 M HC1 with 0.1 M KI at T = 298.15 K and literature data. (C) 2009 Elsevier Ltd. All rights reserved.