The compositions of the leaching residue obtained by chlorination method to extract valuable elements (Ti, Cr, Fe, Mn and V) from vanadium slag were mainly Al₂O₃ and SiO₂ with a small amount of hazardous elements Cr and V. In order to reduce the pollution of V and Cr to the environment, a novel method for nontoxic and efficient recycling of leaching residue was proposed. Mullite with high compressive strength of 133.345 MPa and bulk density of 3.20 g/cm³ was successfully synthesized by using leaching residue as raw material, adding appropriate SiO₂ and roasting at 1600 ℃ for 5 h. The trace element Ti and hazardous elements V and Cr in leaching residue entered the mullite lattice in the high temperature reaction process to form a solid solution, which were stabilized in the mullite phase. The synthesized samples were tested by toxicity characteristic leaching procedure (TCLP) and GB5085.3—2007. The results showed that mullite met the toxic leaching standard and was a nontoxic product.