Biosorption of Zn(II) from aqueous solution by biomass marine alga, namely Gracilaria corticata was investigated in this paper. Four independent variables, including initial zinc concentration (50-150 mg L-1), initial solution pH (3-7), contact time (10-50 min), and biomass amount (1-2 g/100mL) were studied in the biosorption process. Optimization of the process conditions for maximizing Zn(II) removal from aqueous solutions by Gracilaria corticata was carried out using Box-Behnken design, including response surface methodology (RSM) based on 27 different experimental data. The optimal operating conditions for 95.0% removal of Zn(II) were as follows: initial zinc concentration of 100 mg L-1, initial solution pH of 5, contact time of 30.5 min, and biomass amount of 2 g/100 mL. In addition, the equilibrium isotherms were described by investigation of Langmuir and Freundlich isotherms. The Freundlich adsorption isotherm model well matched the experimental data (R2 = 0.981). The kinetic data fitted pseudo-second order model with a correlation coefficient of 0.9953. Gracilaria corticata was found to be well applicable for zinc removal based on the experimental results. Manuscript profile