Silica/zirconia (SZ; Si/ Zr molar ratio = 9/1) membranes having pore sizes in the range of 1∼ 3 nm were prepared by the sol-gel process. Organic/ inorganic hybrid membranes were developed by modifying the surface of the silica-zirconia porous membranes via a gas-phase reaction with trimethylchlorosilane (TMCS) to give a surface that was modified with a monolayer of TMCS. Using nanopermporometry, it was found that the inner surface of membrane pores with diameters larger than several nms were successfully modified with TMCS. TMCS-modified membranes showed approximately the same permeability, Lp, irrespective of water concentration (10 and 100 ppm) in hexane. In contrast, an unmodified membrane, showed a decrease in Lp with increasing water concentration, which was pronounced at low permeation temperatures. This suggests that small amounts of water adsorbed to the inner surface of unmodified silica-zirconia membranes and blocked the permeation of hexane.