Biodegradable blend films from chitosan-tapioca starch were prepared by the casting method. To improve the properties of chitosan–starch blend films, nano graphene was used. The influences of the loading of graphene on the physico-mechanical properties in terms of water vapor transmission rate (WVTR), thermal stability, and tensile strength of the blend films were investigated. Scanning electron microscopy (SEM) and FTIR were used to investigate the surface morphology and molecular interaction of the blend films, respectively. After the incorporation of nano graphene, the blend film from chitosan-starch showed an increase in tensile strength and thermal stability, and a decrease in WVTR and elongation at the break. These results showed that the combination of a tiny amount of graphene presents a promising method for improving the mechanical and barrier properties of chitosan-starch biocomposite films. The SEM observations indicated that a high amount (3 wt.%) of graphene was easily agglomerated. This caused the mechanical properties of the composite films to be reduced. Among the various compositions studied, chitosan-starch film filled with 0.8 wt.% graphene showed superior properties. The structural properties investigated by FTIR showed a clear interaction between chitosan and starch, forming a new material with enhanced mechanical properties.