The phase transformation behavior of the superlattice structure of a CeO2-ZrO2 pyrochlore-type binary compound (CP) was investigated so as to better understand how to improve the thermal stability of such a system. CP was synthesized through high-temperature reduction of a conventional CeO2-ZrO2 solid solution with a 1:1 molar ratio of Ce and Zr. High-resolution transmission electron microscopy and selected-area electron diffraction clearly revealed that the pyrochlore structure of CP transformed to the standard disordered cubic fluorite or tetragonal zirconia structure after having been subjected to a high-temperature durability test; moreover, it was determined that this phase transformation moves inward from the crystallite surface. This discovery suggests a new method by which to improve upon this material for practical applications.