[en] A nuclear fuel pellet comprises crystal particles of UO₂ or (U, Gd)O₂ and glassy or crystalline alumina silicate deposition phase, in which the crystal particle has an average grain size of about 20 to 60μ m. Further, the amount of the pellets having such an average composition that the alumina silicate deposition phase comprises 40 to 80 wt% of SiO₂ and the residue of Al₂O₃ is about 10 to 500 ppm of the total weight of nuclear fuels, and the porosity of the pellet is made to less than about 5 vol%. With such a constitution, solid solubilized state of the nuclear fuel pellet can be improved and characteristics of reducing FP gas releasing rate and improving PCI resistant performance are provided, thereby enabling to cope with increased burn up degree. (T.M.)