Abstract: An Al₂O₃-TiB₂ nanocomposite was successfully synthesized by ball milling of Al, TiO₂ and two B source materials of B₂O₃ (system (1)) and H₃BO₃ (system (2)). Phase identification of the milled samples was examined by Xray diffraction. The morphology and microstructure of the milled powders were monitored by scanning electron microscopy and transmission electron microscopy. It was found that the formation of this composite was completed after 15 and 30 h of milling time in systems (1) and (2), respectively. More milling energy was required for the formation of this composite in system (2) due to the lubricant properties of H₃BO₃ and also its decomposition to HBO₂ and B₂O₃ during milling. On the basis of X-ray diffraction patterns and thermodynamic calculations, this composite was formed by highly exothermic mechanically induced self-sustaining reactions (MSR) in both systems. The MSR mode took place around 9 h and 25 h of milling in systems (1) and (2), respectively. At the end of milling (15 h for system (1) and 30 h for system (2)) the grain size of about 35–50 nm was obtained in both systems.