Abstract: The “click chemistry” reaction was used to solve the problem to remove excess PEG from graft chitosan-mPEG copolymers for synthesis.A series of graft chitosan-mPEG copolymers were first synthesized via “click chemistry” reaction between azido-end monomethoxypolyethylene glycol and alkynyl chitosans that were synthesized by N-alkylation of chitosans with propargyl bromide.The chemical structures of the copolymers were characterized by ¹H NMR and FT-IR and their physical properties were measured by differential scanning calorimetry(DSC) and thermogravimetric analysis(TG).The graft rate of PEG in copolymers was determined to be about 11% with ¹H NMR.The DSC analyses showed that the crystallinity of the copolymers decreased. The TG analyses proved that the thermal stability of the copolymers increased. The graft chitosan-mPEG copolymers may be used as drug carriers.