This study presents, for the first time, the development of all-rye-based nanocomposite films for biobased food packaging by incorporating cellulose nanocrystals isolated from rye bran (RB-CNC) into a rye arabinoxylan (R-AX) matrix. The isolated RB-CNC exhibited high purity (>90% cellulose) and surface charge (-35.8 mV), together with an exceptional aspect ratio (similar to 61) and thermal stability (230 degrees C). Nanocomposite films were developed by incorporating RB-CNC at different loadings (5, 10, and 20 wt %) into commercial R-AX matrix. The resulting composites demonstrated significantly enhanced thermomechanical performance, competitive water vapor permeability, and excellent optical transparency, which are key properties required for packaging applications. Specifically, films with 10 wt % RB-CNC showed an 81% increase in Young's modulus, a 49% enhancement in elongation at break, and a 98% rise in tensile strength compared to neat R-AX films. Optical transparency improved with RB-CNC content, with films achieving 95% transmittance and only 10% haze. All nanocomposites exhibited a thermal stability improvement exceeding 10 degrees C while retaining R-AX's intrinsic water vapor barrier properties. These findings highlight the potential of RB-CNC as a high-performance, biobased reinforcement for hemicellulose-based biopolymers, paving the way for fully biobased, circular food packaging solutions.