A novel method to separate As from high As-Sb dust using Fe2O3 as a fixative under an O-2-N-2 atmosphere is proposed. Here, Sb is oxidised and converted to Sb2O4 and FeSbO4 that remain in the roasted residue, and As is volatilized in the form of As4O6. The Sb2O3 can be selectively oxidised from the dust by using 21 vol% O-2, but the formation of amorphous substance (As-Sb-O) hinders the effective separation of As and Sb. Adding Fe2O3 hinders the amorphous substance formation and destroys the structure of the solid solution ((Sb, As)(2)O-3) in the raw material by converting the Sb component in it to FeSbO4. Therefore, the volatilization rates of As and Sb can reach up to 90.53% and only 13.20%, respectively at a roasting temperature of 723 K, roasting time of 90 min, an Fe2O3 dosage of 15 mass%, and O-2 content of 21 vol%.