Mesoporous MCM-48 silica was synthesized by templating method and the structure of particles was characterized by XRD, TEM and N2 adsorption techniques. The surface modification of particles in order for introducing into PSF matrix was performed by dimethyldichlorosilane (DMDCS) silylation agent. SEM images of as-synthesized and modified MCM-48/PSF MMMs indicate that in the modified MCM-48 silica particles adhered well to the PSF matrix and that the synthesized MMMs were defect free. The incorporation of MCM-48 particles in to the PSF matrix and also surface coating of these MMMs by polydimethylsiloxane (PDMS) were performed. The quality of surface coating was investigated by SEM images and permeability tests. For all gases tested (N2, CO2, CH4 and O2), the permeabilities increased in proportion to the weight percent of MCM-48 present in the film and the calculated CO2/CH4 and O2/N2 selectivities of PDMS coated membranes showed enhancement in ideal and actual selectivities both.