In the present study the ultrasound (US) and ultrasound-assisted hydrogen peroxide, and iron sulfate mediated Fenton process (sono-Fenton) was carried out for the degradation of the Congo red (CR) dye. Degradation rate, COD removal, and degradation mechanism of dye in the combined process were studied and the factors affecting the system performance i.e., pH, initial dye concentration, ultrasonic power, time, and effect of variations in concentrations of hydrogen peroxide and iron sulfate were also investigated. The results showed that the dye degradation and COD removal in the sono- Fenton process was 83% and 89% after 60 min of contact time and the coupling process was more efficient and synergistic compared to the respective individual processes. The extent of CR removal increased with increasing the US power and concentration of FeSO₄, and H₂O₂, to an optimum level but decreased with increasing dye concentration, and the optimum conditions were found as pH = 3.5, dye conc. = 25 mg L^-1, US power = 80 W, time = 60 min, H₂O₂ conc. = 5 mM, FeSO₄ conc. = 25 mg L^-1. As revealed by GC–MS results, the sono-Fenton treatment of CR, for 30 min resulted in the formation of byproducts that were finally degraded to small molecules within 60 min of contact time. The synergy of the sono-Fenton process in comparison to respective individual processes is attributed to the increased generation of ^•H and ^•OH radicals. The study demonstrated the potential use of the combination process ‘sono-Fenton’ for the efficient decontamination of water from dye pollutants.