Multicomponent boron-containing carbide (ie, Zr-Ti-C-B) composites show good ablation resistance. The present work is the first report to introduce the powder fabrication of Zr-Ti-C-B using a new method for solid-state diffusion of boron atoms. First, the nonstoichiometric carbide (ie, Zr0.8Ti0.2C0.8) with carbon vacancies was fabricated by free-pressureless spark plasma sintering. Different boron sources such as B2O3, B, and B4C were used to react with the nonstoichiometric carbide. The Zr0.81Ti0.19C0.86B0.14 can be finally generated through the solid-state diffusion of boron atoms using the B2O3 boron source at 1300 degrees C followed by carbon thermal reduction using the phenolic resins at 1600 degrees C.