To get a gas separation membrane of high performance by a mechanism of surface flow through porous membranes, N-methylpyrrole was polymerized by the chemical oxidative method in the micro-pores of a ceramic filter which had an asymmetric structure. Gas permeation rates of O2 and N2 Were measured with composite membranes using air as feed gas. One of them showed that the gas permeation rate of O2 was 1.31×10−4 (cm3 (STP)·cm−2·s−1 cmHg−1) and the separation factor α(O2/N2), 3.9. The gas permeation rate was compared with that of the Vycor composite membrane reported in the previous paper. The gas permeation rate of the composite membranes obtained in these studies appeared proportional to the inverse of the effective thickness of membrane without reduction of permselectivity. With the composite membrane, gas permeation rate and α were measured from room temperature to 120°C. High permselectivity was found even at 120°C. To make clear the interaction between gas components permeating membrane at the same time, gas permeation rates were evaluated while varying the feed gas pressure for both pure gas and mixed gas (air).