To detect miscibility gap in [(CeO2)(x)(ZrO2)(1-x)](0.8)(YO1.5)(0.2) (x = 0-1), powders prepared by liquid-mixing method were investigated by conventional X-ray diffraction (NXRD) and Synchrotron X-ray diffraction (SXRD). The NXRD pattern of the samples, calcined at 873 K, exhibited a broadened cubic structure without any secondary phases. The lattice constants or samples annealed at different temperatures were determined, and they show linear dependence on cerium content (x) except for 1273 K, which indicates that a complete solid solution can be obtained above 1473 K. The NXRD results on samples annealed at 1273 K exhibit deviation from Vegard's law. The SXRD patterns confirmed the existence of miscibility gap in the samples of x = 0.5-0.8 annealed at T = 1273 K for 778 h.