With careful rational optimization and substantial simplification of the syntheses of the recently reported alloys BiO(ClxBr1"12x), we fabricated, via a very simple procedure and at room temperature, a unique visible-light-driven photocatalyst with superb activity. The alloy BiOCl0.875Br0.125 totally decomposed 15 mg/L aqueous Rhodamine B solution within 120 s upon irradiation with visible light (λ > 422 nm). The transparent substrate acetophenone was also swiftly destroyed under the above conditions. The catalyst maintained partial activity even after switching off the light source. Initial mechanistic studies clearly suggest that the mode of action of these materials is fundamentally different from previously reported photocatalytic mechanisms. Evidently, the putative molecular mechanism does not engage dye photosensitization or oxygen radicals.