The production of the ultra-high-temperature composite Hf4ZrC5 by a single-stage method of electrothermal explosion under pressure was experimentally investigated. The effect of mechanical activation on the characteristics of the reaction powder mixture and the formation of the phase composition of the ceramic composite Hf4ZrC5 was studied. The preliminary mechanical activation of a mixture of Hf, Zr, and C powders in hexane enabled one to obtain the ultra-high-temperature composite Hf4ZrC5 with a particle size of less than 1 µm and a residual porosity of 10‒12%.