Silica-organic hybrid membranes were successfully prepared by a Propyltrimethoxysilane (PrTMOS)/O3 counter diffusion CVD method.Deposition temperatures and O3 flow rate were one of the key parameters to control pore sizes of the membranes.H2, N2 and SF6 permeances through the membranes decreased with increasing deposition temperatures up to 320 ℃.Decomposition of propyl groups on silica surface under O3 atmosphere at high temperature was investigated by using hydrolysis powders of PrTMOS.C-CH3 adsorption by the IR observations showed the maximum for the sample prepared at the 320 ℃ treatment.The low permeances through the membrane deposited at 320 ℃ were due to organic groups in the deposited silica.O3 flow rate was also investigated at the 320 ℃ deposition.The maximum C6H6/C6H12 separation factor of pervaporation separation was 113 through the membrane prepared at 0.4 L min-1 of O3 flow rate.