Wheat-bran cellulose (WC) and microcrystalline wheat-bran cellulose (MWC) were prepared, and edible films containing different ratios of soy protein isolate (SPI) with WC, MWC, and ultrasonic/microwave modified MWC (MMWC) were made by casting. The different proportions and particle size of the fillers (WC, MWC, and MMWC) affected the properties of each of the films. The SPI/MMWC film demonstrated the best properties: MMWC had a smaller particle size and more free hydroxyls on the surface, enabling the formation of stronger intra-molecular hydrogen bonds with SPI that yielded a blend film with a homogeneous, compact structure. The different thermal properties of the films were also mainly attributed to their structures. In addition, FT-IR showed the association between SPI and the fillers, while SEM showed that the surface morphology of the SPI/MMWC film was smoother and more homogeneous. (C) 2012 Elsevier Ltd. All rights reserved.