In the present study, removal of cobalt and nickel (II) ions from aqueous solutions was studied by using pretreated fish bones. The effect of pH, contact time, temperature and metal concentration on the removal capacities of the adsorbent was investigated. The maximum removal capacities for Co and Ni (II) were found to be 83.70 and 58.82 mg/g at optimum conditions (p < 0.05), respectively. The experiments showed that when pH increased, an increase in the removal capacity of the pretreated fish bones was observed. The kinetic results of removal obeyed a pseudo second-order model. Freundlich and Langmuir isotherm models were applied and it can be suggested that the experimental data for the adsorption of Co and Ni (II) on the bone sorbents fit the Langmuir isotherm model. The values of R-L for Co and Ni (II) were found to be 0.50 and 0.25, respectively. The thermodynamic parameters related to the adsorption process such as E-a, Delta G(0), Delta H-0 and Delta S-0 were calculated. Delta H-0 values (positive) of cobalt and nickel showed that the adsorption mechanism was endothermic. Weber-Morris and Urano-Tachikawa diffusion models were also applied to the experimental equilibrium data. Based on the results, it can be concluded that fish bones can be used as adsorbent to remove Co and Ni (II) from aqueous solutions with simple processing.