The interest in biodegradable materials has motivated the use of natural resource capable to produce continuous matrices in order to develop bionanocomposites. Natural fibers (cellulose source) of nanometer size had been studied as a reinforcing material when incorporated to a starch matrix. Therefore, cellulose nanofibers (CNFs) were isolated from unripe banana peel using acid treatment (H2SO4 10%). Banana starch biodegradable films were produced by casting method and the effect of the CNFs incorporation to starch matrix, was investigated. Atomic force microscopy (AFM) topography shows that the structure of film was modified with CNFs incorporation. The roughness level of the CF (control film) and CNFF (film with CNFs) were 4.10 nm and 2.46 nm, respectively. The starch matrix was added with CNFs, which are well dispersed in the matrix and did not agglomerate. But, it can be identified darker points, suggesting that CNFF presents some open and more porous structure zones than the CF. The CF film showed similar density (1.10 g/cm3) and higher moisture (18.7%) and water solubility (31.6%) when compared with CNFF film (1.13 g/cm3, 15.1% and 24.1%, respectively). CNFF film presented a reduction of water content at equilibrium (4.31%), sorption coefficient (0.84), water diffusivity (1.8 x 10-8 mm²/s) and water vapor permeability (7.72 x 10-11 g/s.m.Pa) compared with CF (5.0 %; 1.31; 3.7 x 10-8 mm²/s and 8.02 x 10-11 g/s.m.Pa, respectively). The mechanical properties of films were increased with the CNFs incorporation. CNFF film showed be more rigid because present greater tensile strength (CF = 8.9 MPa; CNFF = 16.7 MPa) and Young’s modulus (CF = 283.7 MPa; CNFF = 706.9 MPa). While films without CNFs were more flexible and, as a consequence of their higher elongation capacity (CF = 78.3% and CNFF = 11.5%). The nanocomposite has potential use in food packaging, since the use of CNFs can promote improvements in barrier and mechanical properties. Cellulose nanofibers isolated from agro-industrial residue (banana peels) offer the potential to reinforce composites of biodegradable polymers, producing a value-added material.