The electrochemical properties of composite films consisting of polyaniline (PANI) and carboxydextran-gold hybrid nanomaterials (carDEX-GNP) as a biofuel cell electrode platform were investigated. First, dextran-gold hybrid nanomaterials were synthesized through a series of surface modification of gold nanoparticles. The composite films were formed on a planar gold electrode through electropolymerization after a simple chemical modification of dextran-gold hybrid nanomaterials with carboxyl groups. Cyclic voltammetry indicated that the composite films retained a redox activity in a neutral pH environment. The PANI/carDEX-GNPs composite films showed electrocatalytic activity toward the oxidation of ascorbic acid, indicating that this composite film is an excellent candidate for a biofuel cell electrode.