A novel (Nd0.2Sm0.2Eu0.2La0.2Dy0.2)2Gd0.5Yb0.5TaO7 high-entropy oxide was successfully prepared through the sol–gel and high-sintering technique. The synthesized powder has a single-lattice structure, and the bulk sample has sole pyrochlore-type lattice. Given the particularity structure and the high concentration of oxygen vacancies caused by ion doping, the (Nd0.2Sm0.2Eu0.2La0.2Dy0.2)2Gd0.5Yb0.5TaO7's thermal conductivity (1.385–1.187W·m−1·K−1) is lower than those of (La1/6Nd1/6Yb1/6Y1/6Sm1/6Lu1/6)2Ce2O7, Sm2Zr2O7, and Sm2Ce2O7. Its excellent phase stability and suitable coefficient of thermal expansion (~10.80 × 10−6 K−1, ~1200 °C) also indicate its potential as candidate oxide for thermal barrier coatings.