Surface-deacetylated chitin nanofiber reinforced chitosan films were prepared. The nano-composite films were highly transparent of approximately 84% at 600 nm due to the nanometer-sized fillers and chitosan matrix, which were embedded in the cavities and on the rough surface of the nanofiber networks. Due to the extended crystalline structure, the nanofibers worked effectively as reinforcement filler to improve the Young's modulus and the tensile strength of the chitosan film. After 10% blending of nanofiber, these properties were increased by 65% and 94%, respectively. Moreover, thermal expansion was also significantly decreased from 35.3 to 26.1 ppm K(-1) after 10% addition of nanofibers. Surface-deacetylated chitin nanofiber and the nano-composite films showed antifungal activity against A. alternata.