The Gd2-xCexZr2-xAlxO7 (0.0 <= x <= 2.0) series was synthesized by the gel combustion method. This system exhibited the presence of a fluorite-type phase, along with a narrow biphasic region, depending upon the Ce/Gd content in the sample. Thermal stability of these new compounds under oxidizing and reducing conditions has been investigated. The products obtained on decomposition of Gd2-xCexZr2-xAlxO7 in oxidizing and reducing conditions were found to be entirely different. It was observed that in air the fluorite-type solid solutions of Gd2-xCexZr2-xAlxO7 composition undergo phase separation into perovskite GdAlO3 and fluorite-type solid solutions of Gd-Ce-Zr-O or Ce-Zr-Al-O depending upon the extent of Ce and Al substitution. On the other hand, Gd2-xCexZr2-xAlxO7 samples on heating under reducing conditions show a phase separation to CeAlO3 perovskite and a defect-fluorite of Gd2Zr2O7. The extent of metastability for a typical composition of Gd1.2Ce0.8Zr1.2Al0.8O7 (nano), Gd1.2Ce0.8Zr1.2Al0.8O7 (heated under reduced conditions), Gd1.2Ce0.8Zr1.2Al0.8O7 (heated in air at 1200 C) has been experimentally determined employing a high temperature Calvet calorimeter. On the basis of thermodynamic stability data, it could be inferred that the formation of a more stable compound in the presence of two competing cations (i.e., Gd3+ and Ce3+) is guided by the crystallographic stability.