A novel composite membrane using polydimethylsiloxane (PDMS) as a top active layer and ceramic nanocomposite as the support layer was developed for the gaseous hydrocarbons separation. For the fabrication of hybrid membranes, nanocomposite technology applied for manufacturing ceramic supports with controllable microstructures. Also, a new method was used for coating a uniform and no penetrated polymeric layer. Top layer of ceramic support with nanocomposite microstructures was fabricated using 5 wt % a-Al2O3-SiO2 bidispersed suspensions with optimum weight fraction of second phase (SiO2) based on the fractional collision frequency theory. PDMS selective layer was coated on the outer surface of the porous ceramic nanocomposite support by dip-coating method. In this respect, the effect of several parameters such as pretreatment temperature, PDMS solution concentration, and number of coated polymeric layers on prepared layers morphology and hybrid membrane performance in the separation of condensable hydrocarbons (iso and n-butane) from hydrogen were investigated. The results showed that the membranes fabricated at 140 degrees C as pretreatment temperature and three polymeric layers by 7, 15, and 15 wt % PDMS concentration, respectively, had a high selectivity (>25 at 2 bar)) in C4H10/H2 separation. (c) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012