(YbxGd1−x)2Zr2O7 (0≤x≤1.0) ceramic powders synthesized with the chemical-coprecipitation and calcination method were pressureless-sintered at 1550–1700°C to develop new thermal barrier oxides with a lower thermal conductivity than yttria-stabilized zirconia ceramics. (YbxGd1−x)2Zr2O7 ceramics exhibit a defective fluorite-type structure. The linear thermal expansion coefficients of (YbxGd1−x)2Zr2O7 ceramics increase with increasing temperature from room temperature to 1400°C. The measured thermal conductivity of (YbxGd1−x)2Zr2O7 ceramics first gradually decrease with increasing temperature and then slightly increase above 800°C because of the increased radiation contribution. YbGdZr2O7 ceramics have the lowest thermal conductivity among all the composition combinations studied.