Polybrominated diphenyl ethers, used as flame retardants are a cause of concern over past several years, due to their toxicity, bioaccumulation and widespread distribution. In this work, the combination of ultrasound and advanced Fenton process was investigated for the degradation of Decabromodiphenyl ether (BDE-209). The effect of pollutant concentration, solution pH, ultrasonic power density and loading of Fenton's reagent on the extent of BDE-209 degradation were studied. The results indicated an enhancement in the degradation of BDE-209 during Sono-Fenton treatment, leading to a complete degradation within 80 min of treatment, whereas only 40% and 25% degradation were achieved during ultrasound and Fenton treatment alone. To understand the degradation mechanism, analytical techniques including High performance liquid chromatography and Gas chromatography mass spectroscopy were employed to monitor the concentrations of parent compound along with degradation products. The degradation mechanism was proposed based on the identified degradation products. Total organic carbon (TOC) analysis demonstrated 60% TOC removal within 80 min of treatment. The obtained results suggest that the initiation of BDE-209 degradation during Sono-Fenton treatment followed thermal decomposition at bubble-vapor interface along with reductive debromination at iron surface, accompanied by oxidative degradation of lower brominated congeners at liquid bulk. This work illustrated an effective method for the removal of BDE-209 and hence providing an efficient wastewater treatment solution for recalcitrant pollutants.