Activated charcoal was prepared and characterized from residues of coconut peel (CACC) to remove by adsorption the Methyl Orange (AM) dye in aqueous solution. The charcoal was activated with phosphoric acid. The morphology and structure of the pores of the carbon obtained were analyzed by Scanning Electron Microscopy (SEM) and a surface analyzer. The adsorption data were evaluated by the BET, Langmuir and Freundlich isotherms, finding the Langmuir type I model. The surface area of the activated carbon was 526 m2/g with a pore volume of 0.234 cm3/g and an average pore diameter of 1.78 nm, according to BET, which indicates the presence of micropores. The calculated thermodynamic parameters showed that the adsorption of the AM dye in CACC is a spontaneous process at room temperature and that physisorption and chemisorption are probably involved. The adsorption tests were followed by UV–visible spectrophotometry. The effects of the adsorbate concentration (AM) and the heat treatment (450–500°C) with an air atmosphere were investigated, keeping constant the stirring time and the H3PO4/sample weight ratio. The results obtained indicate that the activated carbon obtained could be used as an alternative low-cost adsorbent in the removal of AM from effluents in aqueous solution.