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Nonstoichiometric TiC 0.5 and (TiNb) 0.5 powders were prepared by the mechanical alloying process using Ti, Nb, and TiC powders as raw materials. Furthermore, the as-prepared TiC 0.5 and (TiNb) 0.5 powders were used as initial materials to fabricate TiC 0.5 and (TiNb) 0.5 compacts under high pressures and high temperatures (HTHP) of 5.5 GPa and 1200⁻1550 °C for 5 min. Phase identification and microstructure of the mechanical-alloyed powders and the sintered TiC 0.5 and (TiNb) 0.5 compacts were realized by an X-ray diffractometer and scanning electron microscope. The results indicate that the as-prepared TiC 0.5 and (TiNb) 0.5 powders have a similar crystal structure of face-centered cubic (FCC) to TiC. The sintered (TiNb) 0.5 compact has good Vickers hardness (~16 GPa), and notably, excellent fracture toughness (~7.3 MPa·m 1/2 ). The non-stoichiometric compound not only reduced the sintering temperature of covalent compounds, but also greatly enhanced the mechanical properties of the materials. Thus, we have provided a novel synthetic strategy for the production of a compound with high-strength covalent bonds.