Abstract: Removal of heavy metal ions by adsorption is considered to be one of the most important operation for water decontamination. However,the industrial application of this method is limited by the desorption efficiency of adsor- bent. The adsorption and desorption of Cu(II)on Ca-montmorillonite have been investigated in this study. The adsorp- tion capacity and removal efficiency are mainly influenced by the initial concentration of Cu( II) and pH of solution. The maximum removal efficiency of Cu(II) reaches 99% at the initial concentration of 40. 84 mg / L when the pH of solution is above 6. Experimental results indicate that the adsorption reactions of Cu( II) on Ca-montmorillonite agree well with the second-order kinetics and the Langmuir isotherm model. The regression coefficient is above 0. 99 and the adsorption capacity from calculation fits well with the experimental data. Cu( II) on Ca-montmorillonite is easily de- sorbed by the NaCl solution of high concentration and the desorption efficiency could reach to 90% . The montmorillon- ite keeps excellent absorption ability after 4-time consecutive adsorp-tion-desorption. Furthermore,the previous two ad- sorption capacities of montmorillonite after desorption are higher than Ca-montmorillonite because of the easier ex- changeable cation of Na+ on montmorillonite. Samples before and after adsorption or desorption have been characterized by X-ray diffraction,which are consistent with the results mentioned above.