Two types of chitosan (CS), alpha and beta, were blended with different concentrations of starch and cast to obtain films. The addition of 1% glycerol was used as a plasticizer to increase film flexibility. The properties of the obtained films were studied by positron annihilation lifetime spectroscopy, X-ray diffraction, and scanning electron microscopy. The results indicate that pure beta-CS had smaller size free-volume holes with high fractions than pure alpha-CS; this was attributed to the difference in bonding of main chains in beta-CS. The addition of starch (>20% up to 50%) reduced the size of the free-volume holes and increased their fraction because of the close packing of chain segments. The effect of 1% glycerol to the CS starch blends indicated that some modification took place. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 116: 2874-2883, 2010