A combination of ultrasonic and low concentration iron (<3mgL⁻¹) of Fenton process (US/Fenton) has been used to treat wastewater containing Acid black 1 (AB1). The results show that the oxidation power of low concentration iron of Fenton could be significantly enhanced by ultrasonic irradiation. The degradation of AB1 in aqueous solution by US/Fenton can receive better results compared with either Fenton oxidation or ultrasonic alone. Many operational parameters, such as ultrasonic power density, the pH value, the Fe²⁺ dosage, the H₂O₂ dosage, AB1 concentration and the temperature, affecting the degradation efficiency were investigated. Also, the effects of various inorganic anions (such as Cl⁻, NO₃^-, CO₃^2-, etc.) on the oxidation efficiency of US/Fenton were studied. Under the given test conditions, 98.83% degradation efficiency was achieved after 30min reaction by US/Fenton. The effect of various inorganic anions was in the following decreasing order: SO₃^2->CH₃COO^->Cl^->CO₃^2->HCO₃^->SO₄^2->NO₃^-. The results show that the US/Fenton can be an effective technology for the treatment of organic dyes in wastewater.