BACKGROUND: A mesoporous alumina supported nanosized Fe2O3 was prepared through an original synthesis procedure and used as a heterogeneous catalyst for the Fenton process degradation of the model azo dye C. I. Acid Orange 7 enhanced by ultrasound irradiation (US/Fe2O3-Al2O3-meso/H2O2 system). The effect of various operating conditions was investigated, namely hydrogen peroxide concentration, initial pH, ultrasonic power and catalyst loading. RESULTS: The results indicated that the degradation of C. I. Acid Orange 7 followed a pseudo-first-order kinetic model. There exists an optimal hydrogen peroxide concentration, initial pH, ultrasonic power and catalyst loading for decolorization. The aggregate size of the spent catalyst was reduced after dispersion in water by ultrasonic irradiation. A very low level of iron leaching was observed ranging from <0.1 to 0.23 mg L-1. The intermediate products of C. I. Acid Orange 7 degradation were identified using gas chromatography-mass spectrometry (GC-MS). CONCLUSION: The optimal conditions for efficient C. I. Acid Orange 7 degradation were pH close to 3, hydrogen peroxide concentration 4 mmol L-1, catalyst loading 0.3 g L-1, and ultrasonic power 80 W. (C) 2011 Society of Chemical Industry