The thermal decomposition of urania–ceria gel corresponding to the composition U_0.7Ce_0.3O_2+x obtained through external and internal gelation routes were studied using infrared spectroscopy (IR). In the case of externally gelated compound, the gel decomposes with the release of H₂O and NH₃ below 500°C. A part of the NH₃ released is entrapped in the solid and above 500°C self reduction occurs in which U(VI) in the gel is reduced to U₃O₈. The decomposition products were identified to be U₃O₈ and CeO₂. In the case of internally gelated compound, decomposition similar to the one for externally gelated compound occurred below 500°C. Above 500°C the carbon present in the gel reduced U(VI) to UO₂ which formed solid solution with CeO₂ around 650°C.