Simulations were used to study the influence of grain boundaries, in stoichiometric samples, upon uranium and oxygen self-diffusion at 300 to 2100K. The study was carried out for two symmetrical tilt grain boundaries, Σ5 and Σ41, which had two different atomic structures. With increasing temperature, the grain boundary core grew, with an increase of disorder. Self-diffusion near both grain boundaries was studied. It was found that grain boundaries accelerated uranium and oxygen self-diffusion rates up to several nanometres from the grain boundary interface. The uranium and oxygen self-diffusion was anisotropic, with a high acceleration along the grain boundary interface. Using the self-Van Hove correlation functions, hopping mechanisms were identified for Σ41 in all directions while, for Σ5, hopping took place along the grain boundary interface and random diffusion occurred in the perpendicular direction of the grain boundary plane.Self-Diffusion near Symmetrical Tilt Grain Boundaries in UO2 matrix: a Molecular Dynamics Simulation Study. Vincent-Aublant, E., Delaye, J.M., Van Brutzel, L.: Journal of Nuclear Materials, 2009, 392[1], 114-20