The physicochemical changes of silk fibers irradiated with gamma-rays was studied in relation to the amount of absorbed dose in the range 0-21 Mrad. The yellowing index (b/L) suddenly increased at low dose for both raw and degummed silk fibers. An equilibrium value was attained from 10 Mrad upward. The tensile properties were significantly affected by exposure to gamma-rays. Both strength and elongation at break decreased at almost the same rate and extent, attaining a final value that was one-half of the untreated control. The birefringence and isotropic refractive index of exposed silk fibers decreased, the effect being larger in the low dose range, suggesting a decrease of crystallinity and molecular orientation. X-ray diffraction curves, however, demonstrated that the crystalline structure remained unchanged even after exposure of the highest gamma-ray dose. The thermal behavior evaluated by DSC and TMA measurements showed that the gamma-irradiation induced a slight decrease of thermal stability in irradiated silk fibers, this effect being detectable only at 21 Mrad of the absorbed dose. The dynamic viscoelastic behavior suggested that the thermal movement of the fibroin molecules in the amorphous and crystalline regions increased with increasing absorbed dose, attributing to the physicochemical modifications induced by the ionizing radiations.