Abstract: Taking Sm₂O₃, NdO₃, Dy₂O₃, Yb₂O₃, CeO₂ and Ta₂O₅ with high purity as raw materials, (Sm_0.5 Nd_0.5)₃Ce₇Ta₂O_23.5 and (Yb_0.5Dy_0.5)₃Ce₇Ta₂O_23.5 oxides were synthesized by multi-step solid phase sintering at high temperature, and the crystalline structure, micromorphology and thermophysical properties were investigated. The results show that obtained oxides exhibited single fluorite structure. The microstructure was dense, and the interfaces among grains were very clean. The element composition and the atom ratio were consistent with the chemical formula. The thermal conductivity of the two oxides was obviously lower than that of 7YSZ, and the thermal conductivity of (Yb_0.5Dy_0.5)₃Ce₇Ta₂O_23.5 was lower than that of (Sm_0.5Nd_0.5)₃Ce₇Ta₂O_23.5. The thermal expansion coefficient above 900℃ of (Yb_0.5Dy_0.5)₃Ce₇Ta₂O_23.5 was slightly higher than that of (Sm_0.5Nd_0.5)₃Ce₇Ta₂O_23.5, and thermal expansion coefficients at 1 200℃ of two oxides were 12.2×10^-6,12.5×10^-6 K^-1,respectively, which were much higher than 9×10^-6 K^-1 of 7YSZ. The thermal conductivity and expansion coefficient of the two oxides satisfied the requirements for thermal barrier coatings.