Molecular dynamics (MD) simulations of condensable vapor permeation through sub-nano scale pores were conducted for a virtual amorphous silica membrane, prepared by melt-quench procedures. The simulated permeance of C2H6 (T-C = 305 K)-like LJ particles through an 8 Angstrom in diameter pore showed a surface diffusion-like temperature dependency in the relatively high temperature region (400-800 K), while at around 300 K, the permeance decreased with decreasing temperature. That is, a maximum was observed in the temperature dependency curve for permeance. The critical temperature, T-C of the permeating condensable vapor could be a contributing factor in the permeation properties through the micropore. The simulated permeance of C2H6 at 260 K decreased with increasing mean pressure. At low pressure, where micropore filling would not be expected to occur, an almost gas like permeation was observed even at temperatures below the T-C, while under micrpore filling conditions at a relatively high pressure, the permeance abruptly decreased. Adsorption simulations were also conducted on the same unit cell, and the mobility of the adsorbed molecules in the micropore filling phase were smaller than those in the lower density phase. Through this investigation of temperature and pressure dependency of permeance, it can be concluded that the development of the micropore filling phase led to a decrease in permeance, and transport as the condensed filling phase through the micropore was an activated process. (C) 2003 Elsevier Science B.V. All rights reserved.