Montmorillonite (MMT) was modified by bio-inspired polydopamine (PDA) to obtain an exfoliated structure. Then, the modified MMT (MMT-D) and the original MMT were incorporated into starch to fabricate individual composite films. MMT lamellae were mostly intercalated in starch, while those of MMT-D were more likely to be exfoliated and presented better dispersibility, as revealed by the surface morphologies and XRD patterns of the composite films. Although MMT provided greater thermal protection to starch, MMT-D improved the tensile properties of the composite films more effectively. The composite film containing 2% MMT-D displayed a tensile strength as high as 8.1 MPa and a Young's modulus as high as 416.4 MPa, which were 2.1 and 3.8 times the values of the pure starch film, respectively. However, the composite films containing MMT had reduced tensile strength and modulus. This study showed that PDA pre-modification of MMT could improve the performance of starch-based nanocomposites, thus accelerating their acceptance in food packaging applications.