The phase region of cubic perovskite-like solid solutions (a = 8.28–8.40 Å) in the Y2O3–BaO–WO3–CuO system is outlined, and the phase compatibility diagram of the BaWO4–BaCuO2–Y2Cu2O5–“1010” (“1010” = Y2WO6 + Y2W3O12) is constructed.