Abstract: This invention provides nuclear fuel pellets including fission substance of UO.sub.2 or UO.sub.2 having Gd.sub.2 O.sub.3 added thereto, the pellets comprising a satisfactory solid-solution state (homogeneous state), large grain diameters, and a second precipitation phase deposited in grain boundaries, and still having a sufficiently high density. This invention also provides a method of manufacturing the above-described nuclear fuel pellets.The nuclear fuel pellets of this invention comprise UO.sub.2 or (U, Gd) O.sub.2 grains and an aluminosilicate precipitation phase, the precipitation phase being a glass state or a crystalline state, the grains having an average grain diameter of about 20 .mu.m through about 60 .mu.m, the aluminosilicate precipitation phase having a composition including SiO.sub.2 of about 40 wt % through about 80 wt % and Al.sub.2 O.sub.