The structure of and oxygen diffusion in UO2 are studied by the molecular dynamics method in the range of transition to the superionic state (melting of the oxygen sublattice) and near the melting point of UO 2. The temperature dependence of the diffusion coefficient of a doubly charged oxygen ion in UO2 is constructed. In the crystalline state at temperatures between 1800 and 2600 K, this dependence is described by an exponential dependence with a diffusion activation energy of 2.6 ± 0. 2 eV. In the superionic state (2600-3100 K), the activation energy of diffusion of an oxygen anion decreases to 1.88 ± 0.13 eV. In melt (3100-3600 K), the exponential dependence of the diffusion coefficient of O2- persists but the activation energy of diffusion decreases still further, to 0.8 ± 0.2 eV. Our experimental results agree (within the limits of experimental error) with data on oxygen diffusion in the crystalline phase obtained by other researchers.