The binding behavior of sodium dodecyl sulfate (SDS) to cationic chitosan, in the form of a swollen crosslinked film is described. Chitosan films were crosslinked with epichlorohydrin. Binding isotherms were determined potentiometrically. The binding isotherms of the crosslinked chitosan was compared to the binding isotherms of chitosan in free solution. As expected, a more highly cooperative binding phenomena is observed, than for cationic chitosan in free solution. The collapse of the gel occurs at a binding fraction greater than 0.6. The collapsed cationic chitosan/SDS complex is described. The presence of hydrophobic regions within the chitosan-SDS complex was demonstrated with the oleophilic dyes C.I. Disperse Yellow 23 and C.I. Solvent Green 3.