Recently,high-entropy ceramics have attracted considerable attentions because of comprehensive phys-ical and chemical properties of high hardness,fracture toughness,and conductivity.However,as a newly emerging class of materials,the synthesis,performance and applications of high-entropy ceram-ics are subject to further development.Here,we reported a new non-stoichiometric TiC0.4/WC/0.5Mo2C medium-entropy carbide (MEC) with a rock-salt structure.Attributed to the solid solution strengthen-ing and twinning strengthening,the TiC0.4/WC/0.5Mo2C sintered at 1900 ℃ by spark plasma sintering(SPS) shows superior mechanical behaviors of microhardness (21.7 GPa),which exceeds that expected from the rule of mixture (ROM) of three individual metal carbides (19.1 GPa) and good fracture tough-ness (5.3 MPa m1/2).Significantly,the bulk synthesized via high-pressure and high-temperature (HPHT)sintering possesses smaller grain size and shows better comprehensive mechanical properties of micro-hardness (23.7 GPa) and fracture toughness (6.2 MPa m1/2).In addition,the effect of anion vacancies on the thermodynamic stability and synthesizability of TiC0.4/WC/0.5Mo2C was analyzed via quantita-tively calculated entropy.Vacancies could significantly enhance the configurational entropy of mixing of the solid phase.The introduction of vacancy defects may expand synthetic path for entropy-stabilized ceramics,especially for multi-component high temperature refractory ceramics.