The main objective of this study is to optimize a new natural biosorbent for the depollution of contaminated water. This pollution can have adverse effects on both human health and the environment. The subject of our study is to use a natural material, abundant and less expensive, like the Pineapple Bark (PB), for the treatment of colored water by adsorption method. In this case, the adsorptive power of the BP was tested on a cationic dye which is Methylene Blue (MB). Hence, the physicochemical and morphological compositions of PB were characterized by Infrared Spectroscopy (IR) and Scanning Electron Microscopy (SEM). A series of experiments were carried out in order to study the influence of certain parameters on the adsorption capacity in particular: the mass of the adsorbent, the initial concentration of the dye, the contact time, the pH and temperature. The optimum adsorption capacity of MB on PB is in the order of 0.78 mg.g-1 with a removal percentage of 96% for a MB concentration of 20 mg.l-1 an amount of 2 g.l-1 of the adsorbent, pH=6 and a temperature of 20°C. The results show that the kinetics of adsorption of the dye MB by PB is described by the second-order model, also the adsorption isotherms are described satisfactorily by the Langmuir model.