The interaction of the cationic polyelectrolyte chitosan (CHI), of different molecular weights, with two anions, picrate (Pi(-)) and eosin (Eo(2-)), in water was analyzed at pH 2.50 and 5.00. For this purpose the anions transfer current across a water/1,2-dichloroethane interface was employed to quantify anions concentration in absence or in presence of CHI. When CHI was added in increasing amounts to aqueous solutions containing Eo(2-) or Pi(-), a gradual decrease in current values was observed, evidencing the binding of the anions to the polymer. This effect was more important at low pH values and for CHI with the highest molecular weight. From the results it is concluded that the interaction Eo(2-)-CHI is stronger than the corresponding to Pi(-), probably due to the higher negative charge, and therefore the more pronounced hydrophilic nature of the first anion, which could lead to favour the electrostatic interactions with the cationic polyelectrolyte. (C) 2011 Elsevier Ltd. All rights reserved.