Nanocrystalline magnesium ferrite is synthesized by high-energy ball milling. The formation of nanocrystalline ferrite phase is observed after 3 h of milling and its content increases with milling time. The structural and microstructural evolution of the nanophase have been studied by X-ray powder diffraction and the Rietveld method. After 3 h of milling, ferrite phase (mixed spinel) nucleates from the starting alpha-Fe2O3-MgO solid solution. After 5 h of milling, a second ferrite phase (inverse spinel) with a larger lattice parameter emerges and its content grows in parallel with that of the mixed spinel matrix. After 11 h of milling, only a very small amount (similar to 3 wt.%) of the starting alpha-Fe2O3 remains unused. With increasing milling time the type of the cationic distribution over the tetrahedral and octahedral sites in the lattice of the nanocrystalline material changes from a mixed to inverse type. Microstructure characterization by HRTEM corroborates the findings of X-ray analysis. (c) 2005 Elsevier B.V. All rights reserved.