The chelation between O,N-carboxymethyl chitosan (ONCMCh) and zinc sulfate in aqueous solution was studied by kinetic experiments and characterized by inductively coupled plasma (ICP) and UV spectrophotometry. The experimental data indicated that the chelating processes were greatly controlled by the reaction conditions (i.e., reaction time, temperature, and Zn2+ ionic and ligand concentrations). The consequence of chelating Zn2+ onto ONCMCh was the formation of complexes with different solubilities. The favorable complexes for ONCMCh-Zn2+ chelate were at the low zinc ionic and ligand concentrations, as well as at the appropriate temperature. The evidence provided by the kinetic parameters and the changes in zinc concentration by ICP analysis further confirmed the plausible complexing mechanisms. While the formation of water-soluble products was occasioned by the electrostatic attraction mechanism, the water-insoluble products were predominantly formed by chelation of Zn2+ with O,N-carboxymethyl chitosan.