We have attained the thermal-responsive gating membrane with a drastic permeability change by several hundredfold; N-isopropylacrylamide (NIPAM) polymers were grafted on the pore surface by the plasma-induced graft polymerization. In this study, we fabricated the gating membrane using a polycarbonate (PC) substrate with straight cylindrical pores. This substrate can be degraded in a strong-alkaline solution, thus the grafted NIPAM polymer was isolated from the substrate and evaluated. Accordingly, we found the grafted polymer has a high molecular weight (from several hundred thousand to a few million) and the polymer chain density is low at ca. 0.01 chains nm(-2). These results indicate factors significant to drastic pore gating; the pores are fully open in a shrunken state at the low chain density, by the existence of enough space for shrinking grafted polymers. Further, the pores are sufficiently closed by swollen NIPAM polymers with a small number of high molecular weight polymers. From the above, we clarified the relationship between the property of the grafted polymer and the permeation behavior of the thermal-responsive gating membrane for the first time. Moreover, the knowledge obtained in this study can provide useful guideline for clarifying the gating function obtained by other grafting technique. (C) 2010 Elsevier B.V. All rights reserved.