The adsorption capacity of a cationic dye (Methylene blue, MB) from aqueous solution onto activated carbon prepared from sugarcane bagasse pith (Saccharum Officinarum) has been investigated. Activated carbon is prepared from sugarcane bagasse pith (SBP) using chemical activation method. This method involves impregnation with ferric chloride followed by carbonization. Activated carbon FAC-1, FAC-2 and FAC-3 are prepared from sugarcane bagasse pith using different impregnation ratios (SBP: FeCl3). It is found that adsorption of dye is influenced by several parameters such as initial dye concentration, contact time, solution pH, adsorbent dosage and adsorption temperature. Equilibrium adsorption isotherms and physico-chemical properties of the modified pith are investigated. Experimental adsorption data is correlated with Langmuir, Freundlich and Temkin isotherm models. Results of equilibrium experiments indicate that adsorption of methylene blue onto FAC-1, FAC-2 and FAC-3 is better described by Langmuir model and the maximum monolayer adsorption capacity at was 17, 43 and 131 mg/g respectively. The thermodynamic parameters such as change in Gibbs free energy, enthalpy and entropy have also been evaluated and it has been found that the adsorption process was a spontaneous and exothermic in nature.