Using nanotechnology to develop films based on polymer nanocomposites containing nanometric fillers might be a new way to improve the mechanical and barrier properties of a given polymer. Because of their renewability, agricultural crop residues can be a valuable source of cellulose nanofibers. The edible part of the banana fruit constitutes only 12 wt% of the plant; the remaining parts become agricultural waste and cause environmental problems. Therefore, cellulose nanofibers were isolated from banana peel using enzymatic treatment (Xylanase enzyme). New nanocomposites were then prepared from a mixed suspension of banana starch and cellulose nanofibers using the casting method and the effect of the addition of these nanofibers on the properties of the resulting nanocomposites (CNFF) 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 films were 4.10 nm and 16.58 nm, respectively. The starch matrix was coated with CNFs which are dispersed well in the matrix and did not agglomerate. The CF film showed low density (1.10 g/cm³) and high moisture (18.7%) and water solubility (31.6%) when compared with CNFF film (1.25 g/cm³, 16.5% and 31.1%, respectively). CNFF film presented a reduction of water content at equilibrium (2.75%), sorption coefficient (0.66), water diffusivity (2.66.exp-8 mm²/s) and water vapor permeability (6.38.exp-11 g/s.m.Pa) compared with CF (3.30%, 0.84, 4.81.exp-8 mm²/s and 8.02.exp-11 g/s.m.Pa, respectively). The greatest values of tensile strength were obtained with CNFs addition (CF = 8.9 MPa; CNFF = 16.4 MPa) and Young’s modulus (CF = 283.7 MPa;CNFF = 759.6 MPa), showing a tendency to form more rigid films. While films without CNFs were flexible and, as a consequence of their higher elongation capacity (CF = 78.3% and CNFF = 12.6%). Produced films showed a complex structure formed between starch and CNFS resulting in an improvement in mechanical and barrier properties. CNFs offer potential for reinforcing biodegradable composites, producing a material with added value, being indicated for use on food packaging.