Gas-permeable composite hollow-fiber membrane with a three-layered structure composed of a high-density polyethylene (HDPE) porous layer, a MK-2F thin dense layer, and a HDPE porous layer has been successfully developed by melt-spinning and cold/hot stretching. The MK-2F thin dense layer was composed of a poly(ethylenebutylene)-block-polystyrene triblock copolymer (SEBS) phase and a (poly (ethylene-co-ethylacrylate) (EEA)+poly(ethylene-co-propylene) (EPP)) phase. When the stretching ratio was increased, oxygen permeance, f(O2), and nitrogen permeance, f(N2), were linearly increased, while the f(O2)/f(N2) was almost constant at 2.95-3.0. The thickness of a no-pinhole thin layer was 2-5 mu m and its f(O2) was 4.0-8.5 x 10(-6) cm(3) (25 degrees C) cm(-2) s(-1) cmHg(-1). Structural analysis of the thin layer indicated that the SEBS and the (EEA+EPP) formed a 3D-network structure, which restricted elastic recovery of the SEBS matrix and led to the thin thickness. In a pervaporation experiment, the H2O vapor permeation rate of the MK-2F thin layer was about 1/4 that of polydimethyl silicone (PDMS), and the IPA vapor permeation rate was about 1/12 that of PDMS even though the gas permeance of the MK-2F thin layer was almost the same as that of PDMS. (C) 2014 Elsevier B.V. All rights reserved.