Using multilayer composite hollow fiber membranes consisting of a sealing layer (silicone rubber), a selective layer (poly(4-vinylpyridine)), and a support substrate (polysulfone), we have determined the key parameters for fabricating highperformance multilayer hollow fiber composite membranes for gas separation. Surface roughness and surface porosity of the support substrate play two crucial roles in successful membrane fabrication. Substrates with smooth surfaces tend to reduce defects in the selective layer to yield composite membranes of better separation performance. Substrates with a high surface porosity can enhance the permeance of composite membranes. However, SEM micrographs show that, when preparing an asymmetric microporous membrane substrate using a phase-inversion process, the higher the surface porosity, the greater the surface roughness. How to optimize and compromise the effect of both factors with respect to permselectivity is a critical issue for the selection of support substrates to fabricate high-performance multilayer composite membranes. For a highly permeable support substrate, pre-wetting shows no significant improvement in membrane performance. Composite hollow fiber membranes made from a composition of silicone rubber/0.1-0.5 wt% poly(4-vinylpyridine)/25 wt% polysulfone show impressive separation performance. Gas permeances of around 100 GPU for H-2, 40 GPU for CO2, and 8 GPU for O-2 with selectivities of around 100 for H-2/N-2, 50 for CO2/CH4, and 7 for O-2/N-2 were obtained.