Nowadays, most materials used for food packaging are practically non-degradable, representing a serious global environmental concern. Accordingly, edible ?lms based on natural materials are receiving much attention as potential packaging materials, principally due to their biodegradability which is considered to be a promising solution to environmental impacts of synthetic polymer packaging .The production of biodegradable and edible ?lms from proteins can play an important role in food preservation by extending shelf life and improving quality of foods. However, biopolymer ?lms are limited in their ability to obtain wide commercial application due to disadvantages related to performance such as brittleness, poor moisture barrier and mechanical properties. Although plasticizers are generally added into ?lm-forming solutions to prevent ?lm brittleness still researchers are looking for other ways to solve the problem. In this case, cellulose ?bers with one nano/micro scale dimension might be attractive as reinforcing ?llers in polymeric matrices due to their stiffness and good mechanical properties with very high bending strength. To provide cellulose, oat which is an agriculture product and among the other cereals has more husks can be considered as a suitable source. Its husk is an agro-industrial byproduct in huge quantities with about 30-35% cellulose in their cell walls that does not use perfectly. The main goal of this study was the isolation and incoporation of nanocrystalline cellulose (NCC) prepared from oat husk to whey protein biofilm to improve its mechanical properties. In this regard, acid hydrolysis was used in order to isolate of nanocrystalline cellulose from the oat husk. In the first stage lignin and hemicellulose was removed using 1.4% acidified sodium chlorite (NaClO 2 ) and 5% potassium hydroxide (KOH). Later and to reach cellulose nanocrystalline, 65% sulfuric acid was also added during acid hydrolysis process. Composition of the materials obtianed after each stage of the treatments and morphological of NCC were monitored by Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy ( SEM ) respectively. FTIR spectroscopy indicated the progressive removal of non-cellulosic components while SEM photos showed removal of amorphous regions and remainig crystallin regions, caused producing of NCC with a mean width of about 76 nm. Consequently, bionanocomposite film based on whey protein isolate and NCC in percentages of 2.5, 5 and 7.5(w/w) were prepared by casting sollution method and then the reinforcing effects of cellulose nanocrystalline on mechanical properties, water vapor permeability (WVP), thickness, traarency, surface color, moisture content and solubility on the film were studied. Results indicateed all of the composite were in good uniformity and were suitable for evelation mechanical and tensile properties. The films prepared of 5% NCC showed the highest tensile strenght and modulus of elasticity and the lowest elongation at break. Addition of NCC caused lower WVP that could decrease the WVP up to 36%. In terms of exterior characteristics, however, turbidity and total color difference (?E) were increased with increasing of NCC concentration. In total the result showed that isolation of NCC from the oat husk have positive effects on mechanical and barrier properties of whey isolated protein biofilm and help in improving its properties. Keywords: nanocrystalline cellulose, Oat husk, Whey protein Isolate, mechanical properties, Bionanocomposite