[en] A gadolinia (Gd₂O₃)-incorporated pellets have been used so far in order to homogenize the power distribution inside of a reactor and suppress the initial reactivity of fuels of high burnup degree. In the present invention, a Gd₂O₃-incorporated nuclear fuel pellet is constituted as a double pellet structure comprising a pellet of dioxides of at least one of uranium and plutonium at the inner side and a pellet of Gd₂O₃ applied to the dioxide described above at the outer side. Further, it has a double structure comprising high concentration Gd₂O₃ at the outer side and low concentration Gd₂O₃ at the inner side. Furthermore, the crystal grain size of each of the fuel materials is increased, to improve FP gas retainability. (T.M.)