Ceramic powders of ( NdxGd1- x)(2)Zr2O7 ( x = 0, 0.1, 0.3, 0.5, 0.7, 0.9, 1.0) were synthesized by chemical-coprecipitation followed by calcination method, and were then pressureless- sintered at 1,600 degrees C for 10 h in air. Phase constituents and morphologies of the synthesized powders and sintered ceramics were identified by X- ray diffraction ( XRD), scanning electron microscopy ( SEM), and transmission electron microscopy ( TEM). A high- temperature dilatometer and a laser- flash method were used to analyze the thermal expansion coefficient and thermal diffusion coefficient of different ceramics from room temperature up to 1,400 degrees C. Thermal conductivity was calculated from thermal diffusivity, density, and specific heat. ( NdxGd1-x)(2)Zr2O7 ( 0.1 B x B 1.0) ceramics are with a pyrochlore- type structure; however, pure Gd2Zr2O7 exhibits a defective fluorite- type structure. The average linear thermal expansion coefficients of different ( NdxGd1-x)(2)Zr2O7 ceramics decrease with increasing the value of x from 0 to 1.0 in the temperature range of 25 - 1,400 degrees C. The thermal conductivities of ( NdxGd1-x)(2)Zr2O7 ceramics are located within the range of 1.33 to 2.04 W m(-1) K-1 from room temperature to 1,400 degrees C.