A hierarchically structured alpha-Al2O3/Al3Ti composite was fabricated by an in situ process called exothermic dispersive synthesis from a powder blend of Al and TiO2. The microstructure of the composite was investigated by X-ray diffraction, scanning electron microscopy, and X-ray energy dispersive spectroscopy. Three transitional phases, specifically TiO, Ti2O3, and gamma-Al2O3, were found to form during the reactive process. Using differential scanning calorimetry, it was found that the reaction between the Al and TiO2 occurred through three intermediate steps and their corresponding activation energies were 390, 205, and 197 kJ/mol, respectively. Moreover, the reaction rate of the third step was found to be much higher than that of the second step, and the time taken by each reaction step decreased with the increase of the heating rate. The findings are critical to understanding the microstructural development in the synthesis of strong and tough Al2O3/Al3Ti composites.