This study was carried out to find out the relationship between qualities and contraction phenomenon of silk fibers by treatment of concentrated neutral salts. The contraction effects of silk fibers showed the critical point on the treatment conditions of concentration, temperature and time, among three kinds of neutral salts such as calcium nitrate, calcium chloride and lithium bromide. But, The silk fibers, pretreated with bromide and/or formaldehyde, did not show the contraction upon treating with calcium nitrate. This indicates that tyrosine and serine can be correlated with the contraction reaction because of coupling these amino acids with bromide and formaldehyde. In conclusion, a mechanism for the contraction of silk fiber with highly concentrated calcium nitrate solution is supposed as follows. At the initial stage of ration, the water was penetrated into the amorphous regions and fibers swollen, therefore, the contraction took place mainly in amorphous regions, which have plenty of functional groups with hydroxyl residues. Then, as the calcium nitrate is penetrated into the microfibril, the gydrogen bonds of tyrosine and serine residues and broken and crystalline regions are more and more influenced by increasing concentration of calcium nitrate solution. Microgibrils of crystalline regions become entangled, contracted to linear direction and rearranged to form new stable hydrogen bonds.