An attempt to change the structure of silk fibers and their properties for the biological application was studied by utilizing gamma radiation in various Co60 intensities (0 kGy, 30 kGy, 50 kGy, 100 kGy, 200 kGy, 500 kGy, 1000 kGy, 2000 kGy, 3000 kGy). With the increase of the gamma radiation intensity, SEM result shows that cracks and fragments were formed between microfibrils of the irradiated fiber significantly. Simultaneously SDS-PAGE results give the evidence that the molecular weight of the fibroin diminished. Furthermore, the breaking strength and elongation of irradiated fibers decreased gradually with the increasing Co60 intensity. Although no significant changes of the molecular conformations were found by FTIR and X-ray diffraction, the effects on molecular interactions of the silk fibroin, such as peptide bonding, hydrogen bond and intermolecular bonding force, were obviously observed and enhanced gradually with the increase of gamma radiation intensity.