The goal of this work was to investigate the decomposition of C.I. Reactive Orange 107 (RO107) azo dye by advanced oxidizing method, ultrasound. This method can decolorize azo dyes in a short time period at a high energy input. More than 80% of decolorization was achieved within 4h. Degradation of the dye RO107 followed pseudo-first-order kinetics. Effects of operating parameters such as frequency, temperature, and initial dye concentrations were investigated. Sonolysis was also carried out in the presence of tert-butyl alcohol to determine the sonication mechanism. Results showed that sonication is controlled by hydroxyl radicals together with pyrolysis, the effect of which is half of free radical reactions. Dye degradation and formation of intermediates and ions were detected directly or indirectly by high-pressure liquid chromatography-diode array detector and liquid chromatography-tandem mass spectrometry analysis. Sulfanilic acid (m/z:172) was identified as the main dye intermediate. Possible pathways for the formation of the degradation products were proposed. Results are presented that allow insight into the reaction mechanism.