Different treatments applied on cotton fibres influence their thermal behaviour. The chemical structure of the reagents used in the technological process affect the thermal decomposition process. Dyed cotton fibres proved to have a lower thermal stability compared with the white samples [1]. Thermal analysis could be successfully used to determine the nature of different natural cellulosic fibres analysed and the mordant added in the dyeing process. Presence of a fixing colour compound contributes to a high thermal stability of the cotton dyed fabric [2]. The decomposition atmosphere also influences the cellulosic fabric degradation. The activation energy has lower level in oxidative conditions compared with nitrogen. Also the degradation rates are high in air. Those results suggest an advanced thermal degradation process in presence of oxygen [3]. The research data presented in the literature propose the thermal analysis as an important analytical tool to investigate and predict structural properties of different natural fibres. Our study demonstrated the influence of the complexing agents used in the bioscouring process of 100% cotton fabrics. The thermal behaviour investigation was also corroborated with mechanical and other determinations. The reaction was developed in presence of ultrasound in distillate water. The intended purpose of the bioscouring process was the pectin degradation and elimination of different impurities presented in the natural fibres (organic acids, wax, and minerals). For a proper treatment process in the reaction bath were added different quantities of commercial pectinolytic products (Beisol Pro), complexing agents (EDTA or sodium citrate) and a surfactant (Denimcol Wash-RGN detergent from CHT Bezema Company).