Molecular Dynamics (MD) has been used to model oxide ion diffusion along Sigma 5 (310)/[001] grain boundaries in cubic zirconia. Simulations of both pure zirconia and 8 mol% yttria stabilized zirconia (YSZ) over a temperature range of 1273 to 2673 K revealed that while the open grain boundary structure enables oxygen transport to occur, the rate of diffusion is not as rapid as that in the bulk region of YSZ crystals.