Chemically and mechanically stable chitosan and N-acylchitosan were prepared. N-Octanoylchitosan gives the pronounced decrease of water content, whereas N-benzoylchitosan keeps a higher content of water. The equilibrium sorption of various sodium salts was determined and is explained by a dual mechanism, consisting of partition and Langmuir sorption. The characteristics of the membranes and the size of the salt anions clearly influence permeability as well as sorption. Permeation behavior was interpreted by the Teorell-Meyer-Sievers (TMS) theorem. The mobility of anions decreases with Stokes radius, decreasing in the order chitosan > N-benzoylchitosan, N-octanoylchitosan, indicating the effect of the polymer chain molecules, especially a steric obstruction effect on the ion transportation through the membranes. The introduction of the N-acylated hydrophobic group to the charged chitosan membranes appears to enhance permselectivity.