UNLABELLED: This study investigated physicochemical, microstructural, and antibacterial properties of β-chitosan-kudzu starch composite films with addition of 0%, 20%, 60%, or 100% kudzu starch (w starch/w chitosan) in 1% chitosan solution. Molecular interactions between chitosan and kudzu starch and the crystal structure of the films were also determined. Adding 60% kudzu starch reduced water vapor permeability and solubility of pure β-chitosan film by about 15% and 20%, respectively, whereas mechanical strength and flexibility of the film were increased about 50% and 25%, respectively. Micrograph showed that β-chitosan film was totally amorphous, and the composite films generally became rougher with more starch added. Fourier transform infrared and X-ray diffraction spectra showed that the 2 film-forming components were compatible with each other. Pure β-chitosan film resulted in 9.5 and 11.5 log CFU/mL reduction in Escherichia coli and Listeria innocua based on plate count method, respectively. Addition of kudzu starch reduced the antibacterial activity of film, but still achieved 8.3 and 10.3 log CFU/mL reduction in E. coli and L. innocua, respectively when kudzu starch to chitosan weight ratio was 1:1. Reduced antibacterial activity might attribute to the interaction of amino groups in β-chitosan with the hydroxyl groups in kudzu starch. This study demonstrated that kudzu starch effectively improved water barrier of β-chitosan film, and the composite films retained strong antibacterial ability. PRACTICAL APPLICATION: One percent of β-chitosan containing 60% kudzu starch (w/w chitosan) composite films possessed better mechanical and water barrier properties than pure β-chitosan films, and showed strong antibacterial activity against both Gram-positive and Gram-negative bacteria. The films may be used as wraps or coatings to prolong the shelf life of different foods or other similar applications.