The present work deals with the use of Caesalpinia bonducella seed powder (CBSP) as a biosorbent for Ni(II) removal from aqueous solution. The nature and morphology of the sorbent were determined using FTIR spectral, SEM, and EDX analysis. The biosorption characteristics of Ni(II) onto CBSP was investigated as a function of pH, biosorbent dosage, contact time, initial metal ion concentration, and temperature. Langmuir and Freundlich isotherms were used to fit the experimental data. The best interpretation for the equilibrium data was given by the Langmuir isotherm. The maximum biosorption capacity was found to be 188.7 mg/g for Ni(II) at pH 5.0 and at 323 K. The equilibrium biosorption data were well fitted with the pseudo-second-order kinetic equation. The values of thermodynamic parameters (Delta G(o), Delta H(o), and Delta S(o)) indicated that the biosorption of Ni(II) onto CBSP was feasible, spontaneous and exothermic in nature. The FTIR results revealed that hydroxyl, amine, carboxyl, and carbonyl functional groups are responsible for Ni(II) biosorption onto CBSP.