Water-soluble glycol chitosan (GC), having the ability to form a membrane, was modified with 3,3′-dithiodipropionic acid (DTPA), a functional group that causes the thiol ⟷ disulfide transition through redox reaction. The membrane derived from this modified GC was water-insoluble. The permeabilities of KCI and socrose through the GC membrane modified with DTPA (MDTPA), the reduced membrane (MSH), and the oxidized membrane (MSS) were investigated. The permeability through the MSH membrane increased twofold relative to that through the MDTPA membrane, and the MSS membrane showed a 60% decrease in the permeability, which had increased in the case of the MSH membrane. The permeability of sucrose was lower and more changeable than that of KCl. These permeation phenomena were discussed from the viewpoint that the thiol ⟷ disulfide transition is responsible for the water content of each membrane.