The optimization of the adsorption of Ni 2+ from aqueous solutions was investigated by ultrasound-assisted preparation of activated carbon from alkaline impregnated hazelnut shells. To investigate the effects of independent variables such as particle size, ultrasonic power density, impregnation ratio, impregnation time, activation temperature and activation time on the adsorption of Ni 2+ from aqueous solutions, the experiments were designed by using the fractional factorial and central composite design method. Furthermore, the results were modelled statistically and optimized by using constrained optimization technic by means of the Matlab. The ultrasonic irradiation used for the alkaline impregnation into hazelnut shells was found to be beneficial for preparation of activated carbon for use as adsorbents to remove Ni 2+ from aqueous solutions.