B4C–Al2O3 composite powder was produced by aluminothermic reduction in Al/B2O3/C system. In this research, microwave heating technique was used to synthesize desired composite. The ball milling of powder mixtures was performed in order to study the effect of mechanical activation on the synthesis process. The synthesis mechanism in this system was investigated by examining the corresponding binary sub-reactions. The self-sustaining reduction of boron oxide by Al was recognized to be the triggering step in overall reaction.