The objective of the present investigation is apply activated carbon obtained prepared from aguaje seeds (Mauritia flexuosa) for the removal of mercury. Activated carbon obtained was modified with manganese oxide to compare the adsorption capacity between the modified and unmodified carbon. The use of ultrasound in a solution with a pH 9 favored the fixation of manganese on the surface of the activated carbon, which was determined using the techniques of DRX and ICP-OES. The kinetic tests carried out at pH 3,5 (over zero charge potential) with a concentration of 5 ppm of mercury show a higher adsorption capacity at modified carbon at pH 9 in accordance with the pseudo second order model. Adsorption isotherms indicate a predominantly Freundlich behavior.