An efficient and convenient method for degradation of Acid orange 3 (AO3) dye from aqueous solution by combination of Fly ash/H2O2 and ultrasound irradiation is reported. The effects of the relevant operating conditions (pH value, dye concentration, H2O2 concentration, dosage of Fly ash and different reaction system) on the degradation of AO3 were also observed. The combination method was found to be effective and could yield better results than either sonolysis or Fenton-like oxidation individually. Removal of 96% was obtained under the optimum conditions (dye concentration, 100 mg/L; H2O2, 5.4 mM; Fly ash, 2.5 g/L; pH 3, ultrasonic irradiation frequency of 25 kHz, room temperature). The process of the degradation follows Behnajady's kinetic mathematical model.