The variation in physical properties of silk fiber can be brought by various treatments, thus dyeing properties may be varied. In this experimental studies, varied physical propertiles of silk fiber due to twisting and heat treatment were obserbed by moisture regain, density, thermal and infrared spectrophotometric analysis and also some accompanied variation in dyeing properties was investigated by diffusion analysis. The structural variation by the heat treatment seems to be caused by the rearrangement of the hydrogen bond between the molecular chains in fibroin. when the heating temperature exceeds 200$^{circ}$C oxidative degradation of silk occurs, thus the affinity of dye on the fiber decreased extremely.