In this study, mechanochemical reactions in the ternary system of Al–B2O3–C were investigated. The starting materials were activated in a planetary ball mill under Argon atmosphere at different times. X-Ray diffraction and scanning electron microscopy (SEM) methods were used to characterize the products. The results showed that B4C, AlB12, and Al2O3 were formed at least after 4 h of milling. Furthermore, an aluminum borate (9Al2O3.2 B2O3) compound was formed during an aluminothermic reaction, as a by-product that could be diminished substantially by increasing the milling time to 20 h. SEM and TEM micrograph showed that the products were agglomerated and the range of particle size was within 100 nm. A high hardness value of 88 BHN with a compaction strength of 313 MPa can be achieved for the bulk sample sintered at 560°C for 90 min.