The inter-particle relationship effects on a temperature reduction and simultaneity of alpha-crystallite formation during theta- to alpha-phase transformation were examined using DTA, XRD, and TEM techniques. Three powder systems derived from the same theta-powder of average crystallite size 15.2 nm were prepared, with the intention of creating different microstructure for each powder systems as: (1) as received, (2) pre-treated by homogenization with a mechanical stirring accompanied by pH adjustment for dispersion, and (3) homogenized and additionally uniaxial-pressed to compacts with higher bulk density. Activation energies of theta-crystallite growth occurring in the three powder systems were also obtained based on an isothermal model of grain growth rate equation. It is found that the temperature reduction characteristics can be related to the homogeneity as well as the inter theta-Al2O3 crystallite distances behaved by the theta-crystallites. Higher homogeneity and shorter inter-crystallite distance for the theta-powder systems may favor the a-crystallite formation at lower temperatures over a shorter duration of phase transformation. Furthermore, activation energies of theta-crystallite growth can be reduced. And alpha-Al2O3 powders fabricated can be mono-sized and free of vermicular growth. (c) 2007 Elsevier B.V. All rights reserved.