In this paper, the sono-advanced fenton oxidation (ZAFO) of aqueous solutions of azo dye Orange G was performed at an ultrasonic frequency of 358 kHz using the zero valent iron (ZVI) as a alternative catalyst of ferrous salts in a Fenton process. The effects of various factos such as ultrasound, ZVI, ferric iron and H₂O₂ addition were investigated on degradation rate. The degradation products formed during sonolysis, ZVI reduction and ZAFO were analyzed  using powerful analytical techniques such as liquid chromatography-electrospray ionization mass spectrometry (LC–ESI–MS), tandem mass spectrometry (MS/MS), and liquid chromatography with diode-array detection (LC–DAD). In order to resolve the MS and MS/MS spectra obtained, the separation conditions were optimized and the best separation with a Shim-pack XR-ODSⅡcolumn was obained using mobile phase 0.2 % acetic acid/acetonitrile in gradient eluent at flow rate of 0.25 mL/min. Based on ultra-violet and visible spectra, [M-H]^- ions, and tandem mass spectrometry, sevaral new degradation products were tentatively identified in sonolysis,  ZVI  reducation and ZAFO degradation. Based on this degradation product identification a possible multi-step degradation scheme was proposed for ZAFO degradation.