The function of thermal barrier coating is to protect the hot components of advanced aero-engines from hot corrosion and ensures the hot components service in high-temperature environment safely. In general, a low thermal conductivity and a high fracture toughness are the key performance indexes for the selection of novel thermal barrier coating materials. In this work, a high-entropy rare-earth tantalate ceramic of (Y_0.2Dy_0.2Sm_0.2Yb_0.2Er_0.2)TaO₄ (i.e. (5RE_0.2)TaO₄) with the superior properties was synthesized via solid-state reaction. The results indicate that (5RE_0.2)TaO₄ exhibits a low thermal conductivity (i.e., 1.68 W·m^–1·K^–1 @ 900 ℃) and a high thermal expansion coefficient (i.e., 10.0×10^–6 K^–1 @ 1200 ℃). (5RE_0.2)TaO₄ shows a high fracture toughness (i.e., 2.6 MPa·m^1/2) and a low brittleness index (i.e., 2.1 μm^–1/2) because of the unique ferroelastic toughening effect. In addition, (5RE_0.2)TaO₄ also has a promising application prospect as one of thermal barrier coating materials.