The adsorption of Methylene Blue from aqueous solution onto prawn shell (raw sample and acid treated prawn shell) was investigated. The effects of pH, dye and solid concentration and contact time on adsorption were evaluated. Adsorption experiments were analyzed in the light of zeta potential measurements. Experimental data were analyzed using three adsorption kinetic models, of which a pseudo-second-order kinetic model was found to be superior. Experimental equilibrium data were fitted to Langmuir adsorption isotherm model from which the free energy of the adsorption processes was determined. The Fourier Transform Infrared Spectroscopy was used to elucidate the adsorption mechanism.