The biosorption of nickel(II) was studied by using crab shell particles of diameter (d p =0.012 mm) under different initial concentrations of nickel(II) in solution (0.01-5.0 g/l), temperature (20-40 °C), pH (2-6.5), and biosorbent dosages (0.5-10 g/l). The maximum removal of nickel(II) occurred at pH 6.5 and temperature 40 °C for a biosorbent dosage of 6 g/l. The results were modeled by response surface methodology (RSM), which determines the maximum biosorption of nickel(II) as a function of the above four independent variables, and the optimum values for the efficient biosorption of nickel(II) were obtained. The RSM studies were carried out using Box-Behnken design and the analysis of variance confirms the adequacy of the quadratic model with coefficient of correlation R2 to be 0.9999. The quadratic model fitted the data well with Prob>F to be <0.0001, indicating the applicability of the present proposed model. © 2009 Springer.