A study of the thermal stability of the oxygen ion conductor BICUVOX.10 was carried out on small pieces of the polycrystalline material by combined TGA and DTA measurements in air, nitrogen, oxygen and helium. The TGA measurements demonstrated that the weight change was less than 0.1% in the different gases. The DTA curves were practically the same. There is evidence for the occurence of a phase change. TGA curves were also taken on BICUVOX.10, the parent compound Bi4V2O11, and the oxides CuO, B2o2, V2O5. under hydrogen. The comparison of the reduction curves shows that BICUVOX.10 is stable up to about 550C with respect to a direct reduction by molecular hydrogen.