Polysaccharides havebeen associated with different biological functions trough their binding to membranes,but their specific role is still unknown. The aim of this work was to study theinteraction of cationic and anionic polysaccharides with anionic andzwitterionic monolayers, at varying subphase composition, thus analyzing theinfluence of electrostatics. The consequent effect of the polymer-lipidinteraction on the film properties was studied, with special interest in themonolayer rheology. The results indicate that electrostatic interactions playan important role in the polymer-membrane affinity, and that the polymers formeda sub-layer, which increased the shear viscosity of the interface. Theinteracting polymer, even when it did not penetrate the lipid film, induced apolymer-like behavior of the monolayer: the whole film (polymer + lipid) washighly compressible and very viscous, which are characteristics of polymerfilms. As a consequence, the process of domain nucleation was affected andthereby, domains were smaller than in the absence of the polymers, despite theenergetics for phase transition and the stability of each phases were slightlyor not modified.