By following the densification kinetics of nanocrystalline γ alumina and corresponding microstructural evolution we showed that the diffusive transformation gamma-alpha involves several processes such as nucleation of alpha phase, rearrangement of gamma crystallite at alpha seed and grain surfaces, formation of porous alpha alumina monocrystalline colonies. Results concerning the effects of seeding and doping elements on the transformation-densification behaviour of the same γ-alumina raw powder batch are also presented. Doping elements seem to have no influence on nucleation rate but could modify the redistribution rate of the ions during the transformation by short range diffusion of doping elements.