The outstanding efficiency of Fe-based metallic glass powders in degrading organic water contaminants is reported. While the glassy alloy contains 24% chemically inactive metalloid elements, the powders are capable to completely decompose the C32H20N6Na4O14S4 azo dye in aqueous solution in short time, about 200 times faster than the conventional Fe powders. The metastable thermodynamic nature and the particle surface topography are the major factors controlling the chemical performance of the metallic glass. Our findings may open a new opportunity for functional applications of metallic glasses.