In the rapidly evolving aerospace sector, the quest for sophisticated thermal barrier coating (TBC) materials has intensified. These materials are primarily sought for their superior comprehensive thermal characteristics, which include a low thermal conductivity coupled with a high coefficient of thermal expansion (CTE) that synergizes with the substrate. In our study, we adopt a solid-state method to synthesize a series of high-entropy rare-earth cerates: La2Ce2O7 (1RC), (La1/2Nd1/2)2Ce2O7 (2RC), (La1/3Nd1/3Sm1/3)2Ce2O7 (3RC), (La1/4Nd1/4Sm1/4Eu1/4)2Ce2O7 (4RC), and (La1/5Nd1/5Sm1/5Eu1/5Gd1/5)2Ce2O7 (5RC), all sintered at 1,600 °C for 10 h. We thoroughly examine their phase structure, morphology, elemental distribution, and thermal properties. Our in-depth analysis of the phonon scattering mechanisms reveals that 4RC and 5RC exhibit exceptional thermal properties: high CTEs of 13.00 × 10−6 K−1 and 12.77 × 10−6 K−1 at 1,400 °C, and low thermal conductivities of 1.55 W/(m·K) and 1.68 W/(m·K) at 1,000 °C, respectively. Compared to other TBC systems, 4RC and 5RC stand out for their excellent thermal characteristics. This study significantly contributes to the development of high-entropy oxides for TBC applications.