Contaminated waters with synthetic dyes pose health hazards; thereby, it is essential to unveil toxicological actions of such xenobiotics [1] and to optimize the existing processes for dyes removal. In the first part of this study, the interaction mechanism of methylene blue (MB) to human serum albumin (HSA) was elucidated by molecular modelling and spectroscopy techniques. This study was undertaken aiming to disclose molecular interaction insights useful to conceive the toxicological action of the dye. Outcomes of the molecular docking simulation suggested that the main active binding site for MB was pinpointed in the domain II of HSA and, the complex formation was favoured by hydrophobic contacts [2]. The fluorescence and circular dichroism spectroscopic techniques confirmed the real interaction between MB-molecule and HSA-macromolecule. The second part of this work dealt with removal of MB dye from aqueous solutions by complexation-ultrafiltration using poly(acrilic acid) (PAA) as chelating agent. The complexation-ultrafiltration process was modelled and optimized using response surface methodology and desirability function approach. The optimal conditions established in this study implied a polymer to dye ratio equal to r=2.10 and pH 6.52. Under these optimal conditions the maximum rejection efficiency (99.12%) was observed. Additionally, the molecular docking simulation shed light on the interaction mechanism between MB dye and PAA oligomer (Figure).