Abstract In this work, a plain weave composed by 50% polyester and 50% cotton (PES/CO) was functionalized by using two polyelectrolytes, in order to modify its surface to provide a dyeing with an uncommon dye class for cotton and polyester fibers. Several techniques of characterization were used to study the effects caused by the interaction between polyelectrolytes (Chitosan and PDDACl) and PES/CO fabric, such as: X-ray Photoelectronic Spectroscopy (XPS), dye solution drop absorption, Scanning Electron Microscopy (SEM) and whiteness by Berger degree. Good results of dyebath exhaustion with excellent values of color strength were obtained for the samples previously treated with PDDACl and Chitosan polyelectrolytes. These promising results mean the possibility of obtaining distinct and solid colors that cannot be obtained with the use of dispersed/reactive dyes, besides generating a lower energetic cost with the use of lower times and temperatures than those normally used to PES/CO dyeing process.