An analysis of the water permeability of a molecular recognition ion gating membrane was performed. The ion gating membrane shows outstanding water permeability switching properties in response to specific ion concentrations, using an ion-responsive polymer consisting of thermosensitive poly(N-isopropylacrylamide) and crown ether moieties, grafted onto a porous substrate pore surface. To investigate the precise properties of the membrane, a polycarbonate track-etched membrane having straight pores with a narrow pore size distribution was used as the substrate, and the ion responsive polymer was grafted onto its pore surfaces. The gating property of the prepared membrane was examined as a function of temperature, specific ion concentration, and filling ratio. Estimates of pore size and dimension of the grafted polymer were obtained using the Hagen-Poiseuille equation. We found that the grafted ion-responsive polymer shows drastic dimensional changes in response to temperature and specific ion concentrations.