The product of the combustion reaction between CuO and Al induced by high energy ball milling has been characterised by using X-ray diffractometry and scanning electron microscopy. It has been observed that the combustion reaction can be ignited very easily by the ball milling. The reaction product consists of polycrystalline Cu in bulk and particle forms and a large number of nanometer sized spherical Al2O3 particles attached to the surface of the Cu. It has been demonstrated that this microstructure is evolved through rapid solidification of Cu and Al2O3 melts and rapid condensation of Cu vapour. Cu and Al2O3 phases are separated in the reaction product. The reason for this is mainly attributed to the large difference in their density and the shaking force of the ball mill.