?? Using brown fused alumina and top grade bauxite as main starting materials, ultrafine alumina, silica fume, and pure calcium aluminate cement as bonding system, the effects of brown fused alumina and top grade bauxite additions on the properties and microstructure of zero-cement Al2O3–SiO2 castables after dried at 110 ℃ and fired at 1 250 ℃ for 3 h were studied. The microstructure was analyzed and discussed. The results show that the hot modulus of rupture of zero-cement Al2O3–SiO2 castables at 1 250 ℃ is up to 22.1 MPa when the bauxite addition is optimum at 12.5 wt%. The mullite formation mechanism in this castables is dissolution–precipitation mechanism and the hot modulus of rupture of the castables is closely related to in-situ mullite formation. Compared with brown fusedalumina, the top grade bauxite is more helpful to in-situ mullite formation and improvement of hot modulus of rupture of the castables.