Abstract: Ab initio calculation is performed to investigate the uranium solubility in different sites of Gd₂Zr₂O₇ pyrochlore. The Gd₂Zr₂O₇ maintains its pyrochlore structure at low uranium dopant levels, and the lattice constants of Gd₂(Zr_2-yU_y)O₇ and (Gd_2-yUy)Zr₂O₇ are gen-erally expressed as being linearly related to the uranium content y. Uranium is found to be a preferable substitute for the B-site gadolinium atoms in cation-disordered Gd₂Zr₂O₇ (where gadolinium and zirconium atoms are swapped) over the A-site gadolinium atoms in orderedGd₂Zr₂O₇ due to the lower total energy of (Gd_2-yZr_y)(Zr_2-yU_y)O₇.