Solutions of chitosan and carrageenan were co-reacted under various experimental conditions to form water-insoluble precipitates. DR. spectroscopic studies and the counter -ions analyses revealed that the combination of the polyions proceeded through the electrostatic interaction between the - NH+3 of chitosan and the - SO3 of carrageenan, and the mole retios of N/S in the poly-electrolyte complexes (PEC) thus prepared have large scope depending on pH, the degree of deacetyla-tion (DD) of chitosan as well as the mixin ratio of the complexing components. The observation of the PEC by scanning electron microscopy showed that there exist fibrous structures in some PEC depending on such reactive conditions as pH, DD of chitosan related with the charge densities of chitosan chains. The solubility of PEC, which is greatly affected by the DD of chitosans, and the blood compatibility have also been studied.