Abstract: Taking La₂O₃, MgO, SrCO₃, CeO₂ and Ta₂O₅ with high purity as raw reactants, the Sr₃La₃Ce₇Ta₂O_26.5 and Mg₃La₃Ce₇Ta₂O_26.5 oxides were synthesized by multi-step high temperature sintering, and the crystal structure, microstructure and thermophysical properties were investigated. The results show that the obtained oxides exhibited a single pyroxhlore crystal structure; the microstructure was very dense, and the grain boundaries were very clear; the element composition and the corresponding mole ratio were consistent with the corresponding chemical formula. The thermal expansion coefficient of Sr₃La₃Ce₇Ta₂O_26.5 was larger than that of Mg₃La₃Ce₇Ta₂O_26.5, and the thermal expansion coefficients at 1 000℃ were 11.6×10^-6, 11.37×10^-6 K^-1, respectively, which were obviously larger than 9×10^-6 K of 7YSZ; the two oxides had good crystal structure stability at high temperature. The thermal conductivity at 1 200℃ of Sr₃La₃Ce₇Ta₂O_26.5 and Mg₃La₃Ce₇Ta₂O_26.5 were 1.68,1.87 W·m^-1·K^-1, respectively, which were smaller than 2 W·m^-1·K^-1 of 7YSZ; the large ionic radius and atomic mass of Sr²⁺ resulted in the lower thermal conductivity of Sr₃La₃Ce₇Ta₂O_26.5 than Mg₃La₃Ce₇Ta₂O_26.5. The thermal conductivity and expansion coefficient of the synthesized oxides both satisfied the requirements for thermal barrier coating.