In this study, one-dimensional (1D) cellulose nanofibers (CNFs) were used to stabilize the dispersion of two-dimensional (2D) montmorillonite (MMT) plates in aqueous system. Then the prepared MMT/CNF solution was simultaneously merged into water soluble corn starch (CS) to obtain CS/MMT/CNF composite freestanding films through a casting method. The reinforcing effect from building blocks of MMT and CNF, interfacial interactions of hydrogen and covalent bonding together led to enhanced tensile strength and Young's modulus, reduced moisture susceptibility and increased transparency of the ternary CS nanocomposites. These extraordinary properties of the ternary nanocomposites clearly point towards a new strategy for designing and fabricating high-performance starch-based nanocomposites by using binary fillers with different geometric shapes and aspect ratio. This kind of ternary nanocomposite can be widely used in food packing and preservation as a biodegradable and green film.