Biosorption of cadmium (II) ions from aqueous solution onto sea urchin test was investigated in a batch system. Equilibrium, kinetic and thermodynamic studies were conducted by considering the effects of pH, contact time, initial cadmium (II) concentration, biomass loading and temperature. Results showed that the uptake of cadmium (II) ions increased with the increase of pH and biomass loading and decreased with increase of initial cadmium (II) concentration and temperature. Langmuir, Freundlich and Dubinin–Radushkevich (D–R) isotherm models were used to analyze the equilibrium data. Langmuir isotherm model described the experimental data well followed by Dubinin–Radushkevich and Freundlich isotherm models. The maximum biosorption capacity (qmax) is 11.904mg/g at the optimum biosorption conditions.