Aiming to improve the mechanical and barrier properties of starch/chitosan composite films, different content of carboxyl-terminated hyperbranched polyester (HPC) (1.25%, 2.50%, 3.75%, 5.00%, w/w, based on the dry weight of starch and chitosan) was introduced to prepare starch/chitosan/HPC composite films (labeled as SCH). Results from physical performance tests indicate that the inclusion of HPC increases the thickness and density of the composite films, notably enhancing tensile strength while maintaining fracture elongation of the films. Addition of 2.50% (based on the dry weight of starch/chitosan) HPC elevates the tensile strength from 2.26 MPa in the control group to 3.58 MPa, with no significant reduction in fracture elongation (measuring 151.04% and 146.40% respectively). UV-visible absorption outcomes reveal that the introduction of HPC induces strong absorption within the 280-320nm range, with absorption intensity increasing with higher amounts of added HPC. Through comprehensive analysis techniques including FTIR, XRD, SEM, DSC, and TG, it was revealed that strong intermolecular force forms between HPC and starch/chitosan through hydrogen bonding and esterification, resulting in a uniform and dense internal structure, increasing surface roughness and thermal stability. The change in water contact angle on the composite film"s surface is minimal, exhibiting an overall hydrophobic nature (greater than 106°). Additionally, the inclusion of HPC reduces the water vapor permeability of the composite film; the addition of 2.50% HPC decreases vapor permeability from 2.85 to 2.13 g·cm/cm2·h·Pa.