This study is focused on the investigation of moisture uptake properties of chitosan films. The GAB isotherm model is found to fit well to the experimental moisture uptake data obtained at 10, 25, and 37 C. The water vapor permeability is found to increase with temperature. The use of plasticizer enhances the water vapor permeability. Finally, the films have been loaded with ZnO nanoparticles and characterized by X-ray diffraction, differential scanning calorimetry, surface plasma resonance and scanning electron microscopic analyses. The crystal size as determined using Scherrer's equation is found to be around 15 nm. The films have shown excellent antibacterial action against the model bacterium Escherichia coli. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 674-683, 2010