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• Association between quaternary chitosan and alginate were regulated via hydration. • Less hydrated counter anion Cl− bound more strongly to positive groups on polymer. • There was a pH transition point of thermal change of association. • Solution's pH had more effect on the hydration of polymers than counter ions. Studies on interactions between oppositely charged polysaccharides have gathered great interest. We proposed that the association between oppositely charged polymers could be regulated via hydration. A comparison study was carried out by using quaternary chitosan with different counterions(Cl−, Ac−, OH−) and sodium alginate. The results showed that the association between quaternary chitosan with less hydrated counter anion Cl− and sodium alginate was weaker than that between quaternary chitosan with more hydrated counter anion Ac− and sodium alginate. There was a pH transition point of thermal change of association between oppositely charged polymers, as the solution's pH had more effect on the hydration of polymers than counter ions. Further studies showed that a fraction of Cl− was still attracted by polycation in the complex and competed with the interaction of polyanion after complexation. The competitive combination was critical for the property (such as self healing behavior) of the carbohydrate polymer complex. [ABSTRACT FROM AUTHOR]