TG-DTA and high-temperature X-ray diffraction measurements were carried out at temperatures from room temperature to 1623 K under various CO2 partial pressures to study the formation of SrCe1-yEuyO3-x from SrCO3, CeO2 and Eu2O3 and also the reaction of the perovskite, SrCe1-yEuyO3-x, with CO2 gas. For the formation reaction of SrCe1-yEuyO3-x sample, two endothermic reactions are observed at 1198 and 1309 K in DTA curves. The former reaction corresponds to the crystal structural change of the carbonate from orthorhombic to hexagonal phase, whereas the latter one is the endothermic formation reaction of the perovskite together with the decomposition of SrCO3. From the reaction of the perovskite with CO2 gas, it is found that the Eu-doped SrCeO3 sample is less stable than the undoped sample at constant temperature, because of smaller tolerance factor of the former.