Abstract: A way to increase burnup is to diminish the elements internal pressure by an adequate large grain UO₂ pellet structure. In the large grain size UO₂ pellets, fission gas release rate decreases and the element internal pressure increases slowly. The effects of Cr₂O₃ on grain size of UO₂ pellets were investigated in this work. Pure UO₂, doped 0.5% Cr₂O₃ and doped 5% Cr₂O₃ pellets were studied, in the atmosphere of 5%H₂Ar, it was going up to 1 700 ℃ at the heating rate of 10 ℃/min and 5 ℃/min, then sintered for 2 hours or 4 hours. Results show that the grain size of pellets doped Cr₂O₃ increases compared with pure UO₂ pellets. Lower heating rate and longer sintering time can also promote grain growth. The sintering process produces liquid phase sintering, which infiltrates grain boundaries and promotes grain growth.