The preparation of Bi12.5Gd1.5ReO24.5 has been performed by solid-state reaction from Bi2O3, Gd2O3, and Re2O7. The phase has been synthesized for the first time. The X-ray measurements have shown that Bi12.5Gd1.5ReO24.5 has a cubic structure (space group Fm3m). The standard molar enthalpy of formation of Bi12.5Gd1.5ReO24.5 has been determined by solution calorimetry combining the enthalpies of dissolution of Bi12.5Gd1.5ReO24.5 and (6.25Bi(2)O(3) + 0.75Gd(2)O(3) + 0.5Re(2)O(7)) mixture in 2 M HCl along with literature data. It has been determined that the above-mentioned phase is thermodynamically stable with respect to their decomposition into binary oxides at room temperatures. It was established that Bi2O3, Re2O7, R2O3, NH4ReO4 have not reacted at ambient temperatures. It is estimated that this reaction takes place at a temperature about 600 K. (C) 2012 Elsevier Ltd. All rights reserved.