An efficient and convenient degradation of AR 97 (C.I. Acid Red 97) in aqueous solution by the combination of ultrasound and Fenton reagent was reported. The various affecting factors were studied. Under ultrasound, the degradation ratio is 99.9% for the initial concentration of 50 mg L−1 using 1.57 mmol L−1 H2O2, 0.054 mmol L−1 Fe2+ at 40°C within 140 min. The combination method was more effective than sonolysis or Fenton reagent process treatment individually. In the combined process, the effect of the kind of anions (Cl−, SO42−, and H2PO4−) and Fenton‐like reagents (Cu2+/H2O2, Co2+/H2O2, and Mn2+/H2O2) on degradation was also observed. Except for SO42−, others had a negative effect on degradation. © 2009 American Institute of Chemical Engineers Environ Prog, 2010