Poly(ethylene glycol) (PEG)-silk fibroin (SF) conjugate (PEGI-SF) was prepared by the chemical modification of solubilized SF with 2-[O-methoxypoly(ethylene glycol)]-4,6-dichloro-s-triazine (actPEG1), and the physical properties of the PEG1-SF film were studied. The circular dichroism (c.d.) spectrum of the PEG1-SF him exhibited both negative and positive extrema due to a beta-sheet structure. D.s.c. measurements and polarizing microscopic observations at elevating temperature of the PEG1-SF film clarified the thermal behaviour of the PEG1-SF film exhibiting the melting of the PEG chains and the decomposition of SF. In the d.s.c. thermogram of PEG1-SF, the positions of the endothermic peaks due to the melting of the PEG chains and the decomposition of SF scarcely shifted compared to the peak position of actPEG I and the peak position of the SF having a beta-sheet structure, respectively. Judging from these observations, the mutual miscibility between PEG and SF was considered to be poor. The tensile tests of the PEGI-SF and SF films revealed that the PEG-modification of SF improved the elongation at break but reduced the tensile strength. based on these results, a layered structure of the PEG1-SF film was suggested.