Chitosan gel particles were prepared by the suspension evaporation method, and their fundamental adsorption properties have been investigated. The chitosan gel particles were spherical in shape, 150 mum in diameter, and had large macropores, about 2 mum in diameter, formed by the polymer networks. The adsorption properties were evaluated from an interaction viewpoint using anionic surfactants having various numbers of carbon atoms, ethylbenzenesulfonate (EBS), octylbenzenesulfonate (OBS), and dodecylbenzenesulfonate (DBS). The pK(a) values of the amino groups within the gel particles were remarkably small compared with those of chitosan polymer. EBS, with its short hydrophobic chain, was adsorbed mainly by an electrostatic interaction in the pH range 3.0 to 6.0, where the amino groups were dissociated. On the contrary, the adsorption of OBS and DBS, with their relatively long hydrophobic chains, took place via an electrostatic interaction in the pH range 3.0 to 5.0, and then by a hydrophobic interaction in the presence of an electrostatic interaction in the pH range 5.0 to 8.0. We conclude that an electrostatic interaction is essential, even for the adsorption of surfactants having strong hydrophobic interactions.