The objective of this study was to prepare chitosan and starch composite films by the addition of 0–3 wt% graphene nanosheets. The film’s tensile strength (TS), tensile modulus (TM), elongation at break (E), moisture uptake (Mu), and water vapor transmission rate (WVTR) were investigated. The surface morphology of the composite films was studied using scanning electron microscopy (SEM). Regardless of biopolymer type, both the TS and TM of the composite films first increased and then decreased with graphene loading. Composite film made with native (unmodified) starch showed lower TS and TM than those with chitosan. Composite films exhibit lower E values than pure chitosan and starch; this is attributed to the increase in the hardness of the films. SEM micrographs indicated that, the surface roughness and phase separation increased with increasing graphene content. This is due to the aggregation of graphene nanosheets, leading to the reduced compatibility of biopolymers. The addition of graphene considerably decreased WVTR and Mu of the composite films. These results indicated that graphene is a promising reinforcing agent for biopolymer composite films.