In this work, the thermodynamic data for the interactions between various metal ions (Cu²⁺, Fe²⁺, Cd²⁺, Zn²⁺, Ca²⁺ and Mn²⁺) and chitosan were measured directly by Isothermal Titration Calorimetry(ITC). Chitosan [poly (D-glucosamine), >75% deacetylation, 800-2000 cps] was mixed with stock solutions of Cu²⁺, Fe²⁺, Cd²⁺ and Zn²⁺, prepared in 0.1 M HNO₃, and of Ca²⁺ and Mn²⁺, in 0.1 M HCl. ITC directly estimates the binding thermodynamics through the measurement of the energetics of molecular interactions at constant temperature. It provides the number of binding sites, the binding constant, and the enthalpy of binding. We found that in the chelation of most metal ions by chitosan, 1:1 binding of chitosan is more dominant than 2:1, cooperative binding, but vice versa for Zn²⁺ and Cd²⁺. The reactivity between metal ions and chitosan decreases in the order Cu²⁺ > Fe²⁺ > Zn²⁺ > Cd²⁺. The chelation of Cu²⁺ by chitosan shows much higher reactivity when compared to other divalent metal ions (Fe²⁺, Zn²⁺, or Cd²⁺). Four metal ions (Cu²⁺, Fe²⁺, Cd²⁺ and Zn²⁺) that we investigated in this experiment show strong reactivity and stability. In contrast, the interactions between Ca²⁺ and Mn²⁺ and chitosan can almost be neglected.