A polyamphoteric gel membrane with both amino and carboxyl groups was prepared from N-succinyl chitosan and poly(vinyl alcohol). The permeabilities of three kinds of solute with similar sizes and different charged conditions, i.e. anionic benzenesulfonic acid, neutral styrene glycol and cationic theophylline, through the polyamphoteric membrane were investigated in various pH conditions. The permeability of benzenesulfonic acid decreased with increasing pH. This behavior can be explained by the change of the electrostatic interaction between the solute and the polyamphoteric membrane brought about by the change of the membrane charged condition. At pH 3.0 the benzenesulfonic acid showed a large permeability due to the attractive interaction with the cationic membrane, whereas theophylline showed a low value due to the repulsive interaction. Thus, an effective separation among the three solutes was achieved in spite of the similar sizes, which was in contrast to the result that almost the same permeabilities were obtained with a poly(vinyl alcohol) membrane based on only the size exclusion effect. At pH 11.0 the polyamphoteric membrane changed to being anionic and lead to benzenesulfonic acid having the lowest permeability among the three solutes. The partition coefficients were measured for the three solutes in various pH conditions. The tendency obtained was similar to that of the permeability.