Abstract: The aim of this study was to prepare silk fibroin (SF)/chitosan (CS) blend films by a solvent evaporation technique. Influence of CS molecular weights on SF conformation transition and thermal stability of the blend films was investigated. SF conformation in the pure SF film was predominantly random coil form, whereas the SF/CS blend films showed co-existed between random coil and β-sheet form with predominantly β-sheet form. Intermolecular bonds between SF and CS in the blend films can be detected from FTIR spectra and thermogravimetric thermograms resulted in the increase of β-sheet form of SF components and thermal stability of CS components, respectively. The SF conformation changes from random coil to β-sheet forms and the CS thermal stabilities in the blend films increased as the CS molecular weight increased. The all blend film matrices were uniform and homogeneous without phase separation. Different CS molecular weights did not affect film transparency of the blend films.