Solid state reactions and corresponding microstructural evolution of the powder particles during heating Al/TiO2 and Al/V2O5 composite powders produced by high energy ball milling have been studied. It is demonstrated that establishment and refining of the composite structure of the powder particles through milling strongly enhances the reaction kinetics. The enhancement is likely due to the creation of a large area of Al/oxide interfaces and the reduction of the inter-particle spacing of the oxide particles inside the powder particles. Al3Ti or Al3V or other Al rich AlxVy phase is the first phase to be formed from the reaction between Al and TiO2 or V2O5 which starts at a temperature close to the melting point of Al. When the Al/V2O5 composite structure is very fine, gamma-Al2O3 may also form from the initial reaction. The powders must be heated to above 900degreesC in order for alpha-Al2O3 to nucleate. At temperatures above 1000degreesC, Al3Ti is transformed into Ti(Al,O) by reacting with TiO2.