Carbons activated from lignocellulosic residues by pyrolysis and chemical activation by microwaves and evaluating adsorbent capacity with methylene blue were objectives of the work. Optimum pyrolysis conditions: 400 ºC, 30 min, 2 g of precursor, N2 flow of 150 cm3N2/min and heating rate of 20 ºC/min, yields of 33% and %C of 44-68%. Carbons with anionic surface charges, megaporous structures and less active surfaces for adsorption. Optimum conditions for chemical activation by microwaves: 200 W, 4 min, 60% H3PO4 and 200 cm3N2/min, yields 72-96%, with %C 61-68%. Carbons with larger active surfaces, highly developed mesoporous structures, and a greater number of active sites. Chemisorption, limiting step of the process. Microwave radiation produced specific effects on the surface chemistry, increased C/O ratio, decreased functional groups with acidic oxygen, giving basic activated carbons, effective for methylene blue adsorption