In this research, in situ fabrication of Al3V based nanocomposite and its formation mechanism have been investigated. In order to synthesize Al3V/Al2O3 nanocomposite, a mixture of Al and V2O5 powders was subjected to high-energy ball milling and the nanocomposite was produced through a mechanochemical reaction. The produced structure was isothermally heat-treated at 500-600 degrees C for 0.5-2 h under argon atmosphere. In order to evaluate the structural changes during milling and annealing, the synthesized powders were characterized by X-ray diffraction (XRD). Moreover, the powder morphological changes were studied by scanning electron microscopy (SEM). It was observed that the reaction between Al and V2O5 occurred after about 30 min and, the Al3V and Al2O3 were formed in nanocrystalline structure with the continuing mechanical milling. Calculation of adiabatic temperature confirmed that reaction took place in combustion mode. In final stage of milling up to 40 h; it was observed that the Al3V decomposed to Al and V so that the optimum time of milling to achieve fabrication of nanocomposite was determined to be about 20 h. Calculations based on Miedema's model verified partial disordering of Al3V during further milling and annealing of as-milled powder at 600 degrees C led to the ordering of Al3V. The crystallite size of Al3V and Al2O3 after annealing at 600 degrees C for 2 h remained in nanometer scale. So the final product appeared to be stable even after annealing. (C) 2012 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.