A medium-entropy fluorite-structured ceramic of (Y0·25Zr0.25Hf0.25Ce0.25)O2−δ was prepared using a solid state reaction method combined with conventional sintering at 1600 °C for 10 h. This ceramic has uniform elemental distribution without impurity and segregation. The annealing experiment results show a reversible transformation between single phase and double phases in (Y0·25Zr0.25Hf0.25Ce0.25)O2−δ in 800–1600 °C. The reversible phase transformation does not display any obvious influence on the thermal expansion of this sample. The thermal expansion coefficient of (Y0·25Zr0.25Hf0.25Ce0.25)O2−δ is 12.4 × 10−6 K−1 in 100–1500 °C, higher than that of 8 wt% yttria-stabilized zirconia (8 YSZ). Furthermore, (Y0·25Zr0.25Hf0.25Ce0.25)O2−δ possesses a lower thermal conductivity (1.51 W m−1 K−1 at 900 °C) and higher oxygen barrier property compared with 8 YSZ at high temperature. The Vickers' hardness, Young's modulus and fracture toughness of (Y0·25Zr0.25Hf0.25Ce0.25)O2−δ are 10.0 GPa, 193.9 GPa and 1.93 MPa m1/2, respectively. These results demonstrate that (Y0·25Zr0.25Hf0.25Ce0.25)O2−δ can be used as a promising candidate ceramic of thermal barrier coatings.