Abstract: A chitosan-based polymeric nitric oxide donor composition comprising a modified chitosan polymer and a nitric oxide [N2O2] dimer, wherein the nitric oxide [N2O2] dimer is bonded directly to the backbone of the modified chitosan polymer without further binding through a nucleophile residue or moiety. The chitosan-based polymeric nitric oxide donor composition is capable of site specific delivery and controlled release of nitric oxide under physiological conditions. The chitosan-based polymeric nitric oxide donor composition further provides a carrier having medically beneficial properties. A method is further included for preparing a chitosan-based polymeric nitric oxide donor composition comprising reacting a nitric oxide dimer (80-100 p.s.i.) with a modified chitosan polymer in the presence of sodium methoxide at room temperature.