A benzene-permselective silica hybrid membrane was successfully prepared by counter-diffusion CVD using PrTMOS (propyltrimethoxysilane) and O-3 as reactants. Deposition temperatures and O-3 flow rates were important parameters. The H-2/N-2 permeance ratio was 250 through a membrane deposited at 240 degrees C. The pore size of the membrane was estimated at about 0.3 nm from the kinetic diameter of H-2 (0.29 nm) and N-2 (0.36 nm). On the other hand, the N-2/SF6 permeance ratio was 529 through a membrane deposited at 270 degrees C. From the kinetic diameter of SF6 (0.55 nm), the pore size of membranes was estimated as 0.4 0.5 nm. Thus, the pore size of the membranes increased with increasing the deposition temperature up to 270 degrees C. SF6 permeances were proportional to total fluxes of pervaporation (PV) tests. This can be explained by the similar kinetic diameters of benzene (0.58 nm) and SF6. The maximum benzene selectivity over cyclohexane was 113 with the total flux of 2.2x10(-4) kg m(-2)h(-1) through the membrane deposited at 320 degrees C at an O-3 flow rate of 0.4 L min(-1).