This study aims in analyzing, at laboratory scale, the mechanisms and performances of 2,4,6-Trinitrotoluene (TNT) removal from contaminated water using electro-Fenton process. This treatment belongs to the group of advanced oxidation processes (AOPs), regarded as the most effective approach to decontaminate wastewater from persistent and toxic organic pollutants. In this study, the TNT degradation was investigated through high resolution LC–ESI–MS/MS to tentatively identify the aromatic by-products. The proposed degradation scheme shows a complex alternation of oxidation and reduction mechanisms, evidencing the importance of the electrochemical reduction in the whole process. Furthermore, oxidative opening of the highly reduced/oxidized TNT aromatic ring occurred rapidly during the treatment, leading to the transient accumulation of short chain carboxylic acids such as malonic, glyoxylic, oxalic and formic acids. Mineralization occurred but was delayed in front of TNT and carboxylic acids, showing the persistence of some recalcitrant by-products