Mechanochemical reactions involving displacement reactions between a reactive metal and a metal oxide often led to the formation a nanocomposite structure. The Mechanochemical reactions fall into two categories, namely (a) those which occur during the mechanical activation process and there the reaction enthalpy is highly negative (e.g. adiabatic temperature T ad = 1300–1800 K), and (b) those which occur during subsequent thermal treatment and here the reaction enthalpy is only moderate (e.g. T ad 1300 K). The first type of reaction takes place in two distinct modes, i.e., either combustion reaction or a progressive reaction. Whenever a reaction is highly exothermic, it can occur abruptly after a certain time of milling and, once started, it proceeds in a self-sustained way. In this case, the reaction requires a given time to begin. This time is called ignition time and, due to the exothermic reaction, can be determined by an increase of temperature. A number of studies have been focused on the development of A1 2 O 3 /metal nanocomposites by different routes including synthesis of nanometer-sized ?-A1 2 O 3 -M composite (M=Fe, V, Cr, Mn, Co, Ni, Cu, Zn, Nb, Mo, W, Si, Fe) by ball milling of an appropriate metal oxide and Al. In this study fabrication and mechanical properties of alumina-based ceramic matrix nanocomposite reinforced by Mo (15 and 26.6 vol.%) was investigated. Al 2 O 3 -Mo nanocomposite was synthesized by ball milling of aluminum and molybdenum oxide powders mixtures in a SPEX8000 type ball mill. The evaluation of powder particles after different milling times and also after subsequent annealing was studied by x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and differential thermal analysis (DTA). The molybdenum oxide was found to be reacted with Al through a rapid self-sustaining combustion reaction process forming an Al 2 O 3 -Mo nanocomposite powder. After annealing at 800°C for 60min, crystallite size of Mo and alumina remained constant. In addition annealing caused formation of different polymorphic, ?-Al 2 O 3 with a crystallite size of 50nm. The powder particles were consolidated by cold uniaxially pressing followed by sintering in vacuum atmosphere at 1300 ?C and 1400 ?C. Results showed a significant improvement in flexural strength of Al 2 O 3 -Mo nanocomposites in comparison to alumina which increases by Mo content.