The present work demonstrates the preparation of Cassia fistula seeds for producing activated carbon through physical and chemical treatment for the extrusion of Ni(II) ion contaminated aqueous solution. The readily prepared sorbents were characterized using SEM-EDX and FTIR. The surface morphology of sorbents possesses 1 mu m mean particle size with uniform size distribution. Furthermore, optimization of operating parameters such as the pH, initial Ni(II) ion concentration, adsorbent dose, time and temperature were investigated. In isotherm and kinetic aspect, Langmuir maximum adsorption capacity of sulphuric acid modified Cassia fistula seeds was 182.2 (mg/g); obeyed Pseudo first order kinetic model. The Ni(II) ion adsorption system undergoes chemisorption, exothermic, feasible and spontaneous. The excellent properties of the Cassia fistula seeds can be alternate for commercial activated carbon.