Abstract: The preparation of UO₂ microspheres with w(Ti)=0.3% doped titanium by sel-gol method, its microstructure and the grain size by means of the optical microscope and the image analyzer are studied respectively. In addition,we carried out a research on the mechanism of grain growth of UO₂ microspheres doped with w(Ti)=0.3%. Based on the calculation, it is obtained that, at the temperature of 1 250℃ to 1 550 ℃, the average activation energy of the grain growth of Ti-doped UO₂ microspheres, E_a is 232.79 kJ/mol, which is significantly lower than the average grain growth activation energy (E_a0=518.32 kJ/mol). In the late sintering period of Ti-doped UO₂ microspheres(after 1 250℃), there may form U₄O₉ in some parts of the microspheres, accelerating U-atom diffusion rate and the grain growth.