The present study was undertaken to evaluate the adsorption capacity of activated carbon modified by organic ligand for the removal of Manganese ions in aqueous solution. In present work, adsorption of Manganese ions from aqueous medium using coal based granular activated carbon filtrasorb-300 and filtrasorb-820 modified by 1,2-Benzenediamine was used for a surface modification of the selected adsorbent. All adsorption isotherms of metal ion on modified GAC have been determined at p H 5 and temperature 25 ± 1 °C. The adsorption parameters were determined using Langmuir, Freundlich, and Temkin isotherm models. The experimental data were analysed by pseudo first order and pseudo second order kinetic models. Results were found to follow Langmuir adsorption isotherm and pseudo second order equation well.