The modified valonian tannin was prepared through sulfonated-mannich reaction and used to adsorb Cu (II) from the aqueous solutions. The adsorption capacity rapidly reached equilibrium within 2 hours. The effect of pH on adsorption was apparent, the amount of adsorption increased significantly as the pH increased from 2.0 to 4.0 and then leveled off at pH 4.0-6.0. Equilibrium data fitted well with Freundlich isotherm model compared to Langmuir isotherm model, indicating that adsorption takes place on heterogeneous surface of the modified valonia tannin. The adsorption capacity was increased by increasing initial concentrations. The maximum adsorption capacity of cooper ion was determined to be 56.200 mg/g at 100 mg/L concentration.