Abstract: Starch-based films are promising alternatives to petroleum-based packaging materials due to their abundant raw sources, low cost, and biodegradability. However, their practical applications are severely limited by poor mechanical performance and high moisture susceptibility. To address these deficiencies, potato starch/carboxymethyl chitosan (PS/CMCS) composite films cross-linked with adipic acid (AA) at different concentrations (5%, 10%, 15%, and 20%, based on the dry weight of PS and CMCS) were fabricated via a solution casting method. The effects of AA dosage on the chemical structure, crosslinking degree, micromorphology, water resistance, optical and mechanical properties, thermal stability, and antimicrobial activity of the composite films were systematically evaluated. Fourier transform infrared spectroscopy results identified a characteristic ester carbonyl band at 1 717 cm^-1, confirming the successful crosslinking reaction among PS, CMCS and AA molecules. Consistently, the gel content increased from an undetectable level in uncrosslinked films to 76.33% for films modified with 15% AA. Scanning electron microscopy observations revealed that all composite films exhibited dense and homogeneous surfaces without obvious cracks or voids, indicating favorable compatibility among film components. The constructed crosslinked network significantly improved the water resistance of the films. Compared with uncrosslinked films, PS/CMCS films modified with 15% AA presented remarkable reductions in moisture content (from 25.2% to 11.8%), water solubility (from 62.4% to 18.7%), swelling degree (from 372.2% to 97.6%), and water vapor permeability (from 4.36×10^-12 g·cm^-1·s^-1·Pa^-1 to 3.11×10^-12 g·cm^-1·s^-1·Pa^-1), while the water contact angle increased from 52.9° to 71.2°. All crosslinked composite films achieved desirable thickness and opacity. Meanwhile, their tensile strength and elongation at break increased from 16.8 to 22.9 MPa and from 4.4% to 5.5%, respectively. Thermal analysis further indicated that the temperatures of the two major mass-loss peaks increased from 107.6 ℃ to 114.8 ℃ and from 270.6 ℃ to 285.4 ℃, demonstrating improved resistance to water evaporation and thermal decomposition. Furthermore, the 15% AA films generated inhibition zones of 22 mm against Staphylococcus aureus and 21 mm against Escherichia coli, verifying the synergistic antibacterial effects of CMCS and AA. Nevertheless, further increasing the AA concentration to 20% induced molecular aggregation and plasticization, with no additional improvement in gel content, thereby compromising the comprehensive performance of composite films. This study demonstrates that adipic acid crosslinking can effectively enhance the water resistance, mechanical strength, thermal stability, and antimicrobial activities of PS/CMCS composite films. The findings provide new insights and a theoretical basis for the development and application of biodegradable food packaging materials.