Antheraea pernyi silk fibroin (SF)/chitosan blend films were prepared by mixing aqueous solution of A. pernyi SF and acetic acid solution of chitosan. The conformation of A. pernyi SF in blend films was revealed to be a P-sheet structure, mainly due to the effect of acetic acid used as a mixing solvent. According to the Fourier transform infrared (FTIR) spectra, NH groups of SF and C=O and NH2 groups of chitosan might have participated in a specific intermolecular interaction among themselves. The exotherm of SF was not exhibited in blend films due to the precrystallization of SF induced by acetic acid. The blend films showed two distinct maximum decomposition temperatures at around 294 (chitosan component) and 369 degreesC (A. pernyi component), which could be indirect evidences of a phase separation. Scanning electron microscopy (SEM) results confirmed that the phase separation occurred in A. pernyi SF/chitosan blend film. Blending with A. pernyi SF can enhance the thermal decomposition stability of chitosan.