: Whey protein is an amphiphilic macromolecular which acts as a macro emulsifier. These films have poor barrier properties against the entry of water vapor and weak mechanical properties. hydrophobic compounds such as oils and fats are used to improve the film barrier properties. One of these oils is walnut oil that is used in this study. Using of these compounds has a negative effect on the mechanical properties of film. To overcome the weakness of mechanical properties, the use of reinforcements such as nanoparticles and nanofibers is recommended. Cellulose nanofibers desire to show self-aggregation and the film hydrophobicity properties will increase by adding walnut oil. The free radical polymerization of methyl methacrylate monomer was done at presence of cellulose nanofibers by using cerium ammonium nitrate as an initiator. It is necessary to mention that the optimum temperature, monomer concentration, initiator concentration and time for polymerization are respectively 35°C, 10 mmol/gr cellulose nanofibers, 2 mmol / dm3 and 120 min. The yield of grafting onto the surface of cellulose nanofibers was 19.37%. According to the gravimetric analysis, FT-IR spectrum and increasing contact angle from 13° to 74.13° successful grafting onto the cellulose surface was confirmed. Protein films were prepared in various percentages of walnut oil. according the results of cup test to measure water vapor permeation and distribution of oil droplets, film with the best oil percentage with best barrier properties (15% oil) was chosen as control film. then composite films based on whey protein and walnut oil in different percentages of unmodified and modified cellulose nanofibers (5-15% of whey protein) were provided. Addition of unmodified and modified cellulose nanofibers increased of film thickness. Improvement of mechanical properties was observed in the tensile test. Addition of 7.5% surface modified cellulose nanofibers with poly (methyl methacrylate) resulting in an increase of 100% in tensile strength, 140% in the young’s modules and 80% reduction in elongation at break which is relative to the unmodified nanofibers. SEM images showed better adhesion to the matrix with 7.5% modified cellulose nanofibers. Among the composites reinforced with cellulose nanofibers, the least water vapor permeation was observed with the film contains 7.5% of modified cellulose nanofibers which is 64% lower than control film. Traarency of composites film significantly has dropped with the addition of cellulose nanofibers and reducing of film traarency is more with modified cellulose nanofibers. The result of contact angle measurement showed that the film contact angle increased by modification about 32% compared to the sample contains unmodified nanofibers. The lowest water absorption was reported for nanocomposites containing 7.5% modified cellulose nanofibers. Keywords : Bio nanocomposite, whey protein, surface modified cellulose nanofibers, water vapor permeation.