The acacia is a kind of tree with a rapid growth. It is now used in Cote d'ivoire, by the National Center of Agronomic Research (CNRA) through its program "Forest and Environment" to fight against the deforestation and to produce, of the charcoal mainly. But, in order to value this Ivorian biomass too, some activated carbons have been prepared by charcoal, from two species of Acacia (auriculiformis and mangium) following the chemical mode of activation with H3PO4. The adsorbent properties of the activated carbon samples obtained have been studied. These properties have been studied from the isotherms of adsorption of the methylene blue (MB). This allowed determining the types of adsorption: the isotherms of adsorption on the activated carbons auriculiformis are of type L and are compatible with the model of Langmuir and that of Freundlich. The isotherms of adsorption on the activated carbons mangium are of type S, and do not describe in a satisfactory way the model of Langmuir, nor that of Freundlich. The results obtained by adsorption of the MB on the different activated carbons permitted showing that, the carbon auriculiformis activated to 800°C, during 6 hours (CA-A6-800), is the most effective of all the activated carbons, for the elimination of this dye.