Fe-based amorphous alloys (FAAs) are considered a new type of wastewater treatment catalyst. In this study, the degradation performance of Fe–Nb–Cu–Si–B amorphous alloy powders for methyl orange (MO) in an ultrasonic Fenton-like process was studied. The effects of pH, H₂O₂, catalyst dosage, temperature, dye concentration, and ultrasound on the degradation efficiency were studied. At pH 0, the dye solution with the MO concentration of 25 mg L⁻¹ could be completely decolorized by 0.07 g FAA powders within 3 min and the reaction rate k was 0.864 min⁻¹. In addition, FAA powders could be recycled 11 times, and the powders after 11 cycles remained amorphous. EPR experiments proved that ˙OH and ˙O₂⁻ were the main reactive radicals. The successful use of the amorphous alloy in the ultrasonic Fenton-like reaction for the first time suggests its potential application as a promising new method for the degradation of azo dyes.