HTGR(High Temperature Gas-Cooled Reactor) is highlighted to next generation power plant for producing the clean hydrogen gas. In this study, the spherical UO₂ kernel via UO₃ gel particles was prepared by the sol-gel process. Raw material of slightly Acid Deficient Uranyl Nitrate (ADUN) solution, which has pH = 1.10 and [NO₃]/[U] mole ratio = 1.93, was obtained from dissolution of U₃O 8 powder with conc.-HNO₃. The surface of these spherical UO₃ gel particles, which was prepared from the broth solution, consisted of 1 M-uranium, 1 M-HMTA, and urea, were covered with the fine crystallite aggregates, and these particles were so hard that crushed well. But the other UO₃ gel particles prepared with the broth solution, consisted of 2 M-uranium, 2 M-HMTA, and urea, have soft surface characteristics and an amorphous phase. This type of UO₃ gel particles is some chance of doing possibility of high density from the compaction. The amorphous UO₃ gel particles was converted to U₃O 8 and then UO₂ by calcination at 600℃ in 4%-H₂+N₂ atmosphere.