In conclusion, a novel water-soluble chitosan grafted with hydrophilic aliphatic polyester was synthesized in a homogeneous and green medium. PBT with pendant hydroxyl groups was grafted onto chitosan resulting in the good solubility of grafting copolymer in neutral aqueous solution, and the improved solubility of the copolymer in water may provide great potential in a number of applications such as cosmetics, pharmaceutics and biotechnology.