Abstract: Natural organisms exhibit excellent mechanical properties due to hierarchical ordered structure and complex organic/inorganic interface interaction. However, the synthetic materials have proven to be difficult to achieve the synchronous improvement of strength, toughness and elongation at break, by merely mimicking their component and structural. Herein, the hybrid films of montmorillonite-cellulose nanocrystal/poly(vinyl alcohol) (MMT-PCNC/PVA) were prepared by electrostatic self-assembly and solvent evaporation. TEM was used to track the formation process. The results of FTIR spectra show that there are multiple weak interactions such as electrostatic and hydrogen bonds in the composite films. The effect of the proportion of MMT and polyethyleneimine (PEI) modified PCNC on the mechanical properties of the composite films was studied. As a result, it is most obvious when the mass ratio is 1∶1 and 1∶2 of MMT and PCNC can drastically enhance the tensile strength (196% for 1MMT-1PCNC/PVA), elongation at break (175% for 1MMT-2PCNC/PVA), and toughness (900% for 1MMT-2PCNC/PVA), which are superior to the pure PVA film. The multiple types of interactions between nanoscale building blocks improve the efficiency of load transfer and cause crack deflection, which result in a highly energy consumption and excellent mechanical properties (such as strength, toughness).