The flexible and transparent composite films were fabricated by a mixture of silk fibroin (SF), poly(ethylene glycol), and mulberry cellulose nanowhiskers (CNWs). The CNWs were uniformly dispersed in the matrix when its content was as high as 12 w/w%. The tensile properties of composite films generally depended on the nanowhisker content, but significantly improved when compared to the pure SF film. DMA analysis revealed that the alpha transition temperature increased gradually with the increase of nanowhisker content, probably due to the formation of interactions between the nanowhiskers and the SF molecular chains, leading to the mobility reduction of the amorphous SF. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012