A model of oxygen 18O tracer diffusion in a growing polycrystalline oxide film with parallel grain boundaries was developed. The basic equations of the model were solved numerically using the Monte Carlo approach. A simulation technique was introduced that took account of the finite-size effect, the film growth, the effect of the oxygen chemical potential gradient across the film, and other factors. This technique was applied to the simulation of the most important cases encountered in two-stage oxidation experiments. The oxygen tracer profiles obtained demonstrate good agreement with the previous theoretical analysis and exact analytical solutions when available. Monte Carlo Simulation of Oxygen Tracer Diffusion in a Growing Oxide Film. Y.Mishin, J.Schimmelpfennig, M.Göbel, G.Borchardt: Defect and Diffusion Forum, 1997, 143-147, 1225-30. See also: Journal de Physique III, 1997, 7[9], 1797-811