Titanium diboride TiB2 and TiAl aluminide composites reinforced with in situ borites have been synthesized from the elemental powders of Ti and B, and Ti, Al and B respectively using mechanical alloying technique. No progressive diffusion between Ti and B was observed. The formation of TiB2 was found to be governed by strong and fast exothermic heat release. This indicates that the formation of TiB2 compound in local area of mechanically alloyed powder generated high energy which in turn ignited and promoted the formation of new compound in the rest of the area. Because of the presence of Al in Ti-Al-B system, the concentration of Ti or B was diluted. The exothermic reaction between Ti and B was consequently delayed. However, grain refinement of Ti and Al in this system down to nanometer scale is faster than that in Ti-Al system due to the contribution of B. Using X-ray analysis, strong but broad TiAl, and weak TiB and TiB2 peaks had been detected at 50 h of mechanical alloying indicating the formation of nano TiAl composite reinforced by TiB and TiB2. However, TiB was, however, not a stable phase; it later was transformed into equilibrium phase of TiB2 after annealing at 800 degrees C.