<p>The rapid growth of the textile industry and the prevalence of fast fashion have generated vast amounts of waste textiles, posing significant environmental challenges. Decolorization is a vital step in the recycling and reuse of colored waste textiles. However, conventional textile decolorization methods often pose serious environmental and water resource pollutions. This study aims to develop an efficient and eco-friendly Fenton-assisted decolorization method to remove reactive dyes, specifically reactive blue 21, from waste cotton fabrics to facilitate recycling and reuse. The decolorization process involved a two-step approach: pre-treatment with thiourea dioxide and ferrous ions (Fe²⁺), followed by oxidative decolorization using hydrogen peroxide (H₂O₂). Parameters such as agent dosage, initial solution pH, temperature, and duration were optimized to achieve high decolorization efficiency while maintaining fabric strength. The optimized process achieved a decolorization rate of over 90%, with minimal tensile strength loss within 10%. Characterization techniques including Fourier Transform Infrared Spectroscopy, X-ray Diffraction, Thermogravimetric Analysis and Scanning Electron Microscopy revealed the structural and chemical transformations in the cotton fibers, providing insights into the decolorization mechanisms. The method also demonstrated high applicability across a range of reactive dyes, particularly azo-based dyes. This research highlights the potential of the proposed Fenton-assisted method for scalable application in textile recycling, offering a sustainable solution to address decolorization challenges in waste cotton textiles while maintaining fiber quality.</p> Graphical abstract <p></p>