Mechanical treatment of aluminium with 10-30 wt% graphite in the high-energy vibration mills leads to the formation of a chemically active substance. The structure of active aluminium and its formation are investigated by X-ray diffraction, adsorption, chemical analysis, and DSC. The reactivity of active Al is checked in reactions with graphite, as well as water, oxygen, and nitrogen. At the initial stage of mechanochemical interaction of aluminium with graphite, the dispergation of components and accumulation of defects in Al and C take place. Simultaneously, the surfaces of aluminium nanoparticles are covered with the carbon layer. Then the chemical interaction of aluminium with carbon starts on the surface of particles. At the final stage, aluminium carbide is formed in the volume of particles. The maximal reactivity of Al corresponds to the Al/C nanocomposites, in which chemical interaction of components is not yet realized. The reactivity of mechanochemically activated aluminium significantly exceeds that of standard aluminium powders. Interaction of activated Al with carbon takes place at 450degreesC, which is 800degreesC lower than the temperature at which the nonactivated aluminium reacts with carbon. Two types of reactions ("isothermal" and explosive) are observed for mechanochemically activated Al with water and air. (C) 2004 Kluwer Academic Publishers.