Structural changes of tussah (Antheraea pernyi) silk fibroin films induced by heat treatment were studied as a function of the treatment temperature in the range 200-250 degrees C. The DSC curve of tussah films with alpha-helix molecular conformation displayed characteristic endo and exo peaks at 216 and 226 degrees C, respectively. These peaks first weakened and then completely disappeared after heating at 230 degrees C. Accordingly, the TMA thermal shrinkage at 206 degrees C disappeared when the films were heated at 230 degrees C. The onset of weight loss was monitored at 210 degrees C by means of TG measurements. X-ray diffraction profiles gradually changed from alpha-helix to beta-sheet crystalline structure as the treatment temperature increased from 200 to 250 degrees C. On raising the heating temperature above 200 degrees C, the intensity of IR and Raman bands characteristic of beta-sheet conformation increased in the whole ranges of amide and skeletal modes. The sample treated at 200 degrees C showed a spectral pattern intermediate between alpha-helix and beta-sheet molecular conformation. The IR marker band for random coil structure, still detectable at 200 degrees C, disappeared at higher treatment temperatures. Spectral changes attributable to the onset of thermal degradation appeared at 230 degrees C.