Slag from aluminothermal reduction of niobium meets the requirements imposed on the raw material for corundum refractory materials. Stabilization of the phase composition and the structure of the slag powder occurs in firing up to 1100°C. The low strength of 5-0.315 mm fraction grains is caused by oxidation of Nb localized in the volume and is eliminated by impregnation with orthophosphoric acid and subsequent heat treatment. A feature of the Al2O3-Nb2O5-H3PO4 refractory mixture is the low degree of crystallization and the formation of monosubstituted aluminum bihydrophosphate characteristic of aluminophosphate and aluminochromephosphate binders with increased adhesion. An optimum slag-base composition of refractory material with an 0.155 ratio of the weight shares of Nb and Nb2O5 was selected.