The chemical state and local structure around zirconium ions in doped α-polycrystalline alumina (300 wt ppm ZrO2) was studied by X-ray absorption spectroscopy measurements at the zirconium K edge and by scanning transmission electron microscopy on thin foils. The zirconium segregation in alumina grain boundaries depends on alumina grain size: for a mean grain size of about ∼3·5 μm, the grain boundaries are saturated with zirconium. The zirconium grain boundaries to bulk concentration ratio, calculated from energy dispersive X-ray spectrometry measurement on thin foils is equal to ∼(5±3)×103. The zirconium located in grain boundaries forms nanocrystalline tetragonal zirconia particles. This allotropic zirconia form is stabilised at room temperature because of the important contribution of the surface free energy.