High C3H6 permselective silica hybrid membranes were successfully prepared by counter diffusion CVD. Propyltrimethoxysilane (PrTMOS), phenyltrimethoxysilane (PhTMOS) and hexyltrimethoxysilane (HTMOS) were employed as silica precursors. C3H6/C3H8 permeance ratio was 414 (C3H6 permeance 1.0 x 10(-8) mol m(-2) s(-1) Pa-1) through the membrane deposited at 450 degrees C for 5 min by using HTMOS as silica source. The optimum deposition temperature was 450 degrees C for the HTMOS/O-2 system to obtain a high C3H6 permselective membrane. HTMOS was selected from among the three silica precursors due to its high thermal stability. N-2/SF6 permeance ratio decreased from 64 to 12 with increasing deposition period from 5 to 90 min. N-2/SF6 permeance ratio showed the maximum at 2.2 x 10(5) through the membrane deposited at 450 degrees C for 5 min.