<p>The kinetics of Fe-Mg interdiffusion in nominally dry polycrystalline olivine was investigated at 6 GPa and 1373–1673 K using diffusion couples of forsterite (Fo₁₀₀) and olivine (Fo₉₀) aggregates. Diffusion profiles were measured by electron microprobe, and diffusion data were analyzed by the Boltzmann-Matano method. Our results show that the Fe-Mg interdiffusion coefficient (<i>D</i>_Fe-Mg) depends on the iron content (with X_Fe ranging from 0 to 0.1). The temperature dependence of <i>D</i>_Fe-Mg in olivine can be described by the Arrhenius relation. By combining the present data and a simple model, it is found that the length scale over which the chemical heterogeneities are homogenized by Fe-Mg interdiffusion in the upper mantle is very limited at the geological time scale, only through solid-state diffusion.</p>