a-keratose, microfibril helix component of wool keratin. was obtained by fractionating the wool keratin oxidized with performic acid. Chitosan samples were heterogeneously depolymerizcd with hydrogen peroxide to control the molecular weight(Mv= 591$ imes$103~ 19$ imes$103) Highly deacetylated chitosan samples were also prepared and these were N-acetylated with acetic anhydride to control the degree of deacetylation(97%~43%). The formation behavior of polyelectrolyte complex(PEC) between the a-keratose and the chitosan with the different molecular weights and degree of deacetylations was examined with a turbidimetric measurement. The mixing ratio(Rmax) at maximum turbidity changed from 0.08 to 0.21 with the degree of deacetylation of the chitosan regardless of the molecular weight difference. The composition ratio was determined from sulfur content of the insoluble PEC isolated near the Rmax. The composition ratio observed was well agreed with the Rmax value observed. On the other hand, the theoretical composition ratios of the PEC formed by the stoichiometric reaction were much higher than those observed. This discrepancy seems to be ascribable to the chain rigidity(conformational hindrance) of the chitosan and the intermolecular or intramolecular ionic linkage owing to the coexistence of oppositely charged NHl+ groups in the a-keratose molecules. Additionally, the erects of ionic and hydrogen bonds-breaking agent on the PEC formation were examined by measuring the transmittance of reaction mixture on the basis of the change of electrostatic and hydrogen bonding forces probably responsible for the chitosan-n-keratose complex formation reaction.