In this study, Ce_1-xSm_xO_2-x/2 ceramics were synthesized by sol–gel route and solid state sintering method. The phase structure was analyzed by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and Raman spectroscopy. The morphologies of the synthesized powders and the corresponding bulk samples were observed using scanning electron microscopy (SEM). Their thermal diffusivities and thermal expansion coefficients were measured by the laser-flash method and the pushing-rod method, respectively. Results show that pure Ce_1-xSm_xO_2-x/2 powders with single fluorite structure are synthesized successfully, and their microstructures of the corresponding bulk samples are very dense. With the increase of Sm₂O₃ content, their thermal expansion coefficients decrease due to the higher electro-negativity of Sm³⁺ ions as compared with that of Ce⁴⁺ ions. Their thermal conductivities at 1000 ℃ lie in the range of 1.62–2.02 W/(m·K) due to the phonon scattering caused by the substituted atoms and oxygen vacancies. The Ce_1-xSm_xO_2-x/2 ceramics can be used as ceramic candidates for novel thermal barrier coatings (TBCs).