Asymmetric poly[1-(trimethylsilyl)-1-propyne] (PTMSP) composite membranes having silica on one side, which were prepared in this study, have been examined for the enrichment of aqueous ethanol solutions using the pervaporation method. FTIR spectrum and SEM pictures have been taken to characterize the membranes. Sorption isotherm measurements were also made to elucidate the impact of silica on PTMSP. While PTMSP considerably swells with ethanol, no swelling has been observed with water. However, the silica-containing membranes have shown a greater degree of swelling in dilute ethanol solutions because of the high affinity of the silica to water. All of the membranes preferentially permeated ethanol, although the permeation rate and the permselectivity altered with the silica content of the membrane and with the amount of ethanol in the feed. A large amount of silica on PTMSP creates an effect like "scaling" and reduces the ethanol uptake of the membrane. The membranes having medium and low silica content exhibited high separability for dilute and medium ethanol concentrations. The pervaporation behavior of all of the membranes conforms with their swelling behavior.