Oxygen diffusion in the oxygen ionic conductor yttria-stabilized zirconia is investigated by means of the molecular dynamics simulation technique. Oxygen ions migrate by means of a discrete hopping process, mainly between neighbouring tetrahedral sites. Diffusion appears to occur in a short time and a long time regime. Only when the oxygen ions have moved over distances much larger than the characteristic distances of the underlying crystal structure, a linear relation is found between the mean square displacement and time. The oxygen tracer diffusion coefficient, obtained from this long time regime, is 1.86 x 10−6 and 3.23 x 10−6 cm2/s at 1759 and 2057 K, respectively. The ionic conductivity, calculated from the tracer diffusion coefficient, agrees well with experimental values.