Novel chitosan (CS)/oxidized starch (OST)/graphene oxide (GO) nanocomposites (COST/GO-n) films are prepared in a casting and solvent evaporation method. Fourier transform infrared spectroscopy, X-ray diffractions, atomic force microscopy, scanning electron microscopy, transmission electron microscopy, thermal gravimetric analysis, tensile testing, and moisture uptake are used to study the structure and properties of these nanocomposites. To indicate the effect of carboxyl groups of OST, some results of the properties of CS/starch/GO nanocomposite (CST/GO-n) were selected for control experimentation. Compared with the control CST/GO-n series, COST/GO-n films, which have the same component ration showed higher tensile strength (sb) and lower elongation at break (eb). Additionally, in the COST/GO-n series, the sb increased with an increase of GO loading. However, higher proportion of GO could result in aggregations of GO nanosheets and deterioration of the film properties. Compared with the COST/GO-0, the values of sb and water resistance of the COST/GO-4 containing 2.0 wt % of GO were improved by 57.7 and 20.1%, respectively. (c) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012