A series of complex rare-earth zirconates (MgxLa0.5−xSm0.5)2 (Zr0.7Ce0.3)2O7−x (x=0, 0.1, 0.2, 0.3) ceramics for thermal barrier coatings (TBCs) were synthesized by coprecipitation–calcination method. Their phase composition, microstructure, and the thermophysical properties were investigated. The results showed that single-phase (MgxLa0.5−xSm0.5)2(Zr0.7Ce0.3)2O7−x (x=0, 0.1, 0.2, 0.3) with pyrochlore structure were prepared, and the microstructure of the products were dense. The thermal conductivity of the ceramics remarkably decreased through doping up to x=0.2 with a minimum value around 1.57 W·(m·K)−1. As a function of increasing x, the thermal expansion coefficient of (MgxLa0.5−xSm0.5)2(Zr0.7Ce0.3)2O7−x decreased firstly and then increased. The maximum value (11.3 × 10−6 K−1) was achieved for the sample with the same composite point x=0.2. These results imply that with respect to thermal properties the optimum material is (Mg0.2La0.3Sm0.5)2 (Zr0.7Ce0.3)2O6.8 for the ceramic layer in TBCs system.