This paper presented the application of polymeric membranes for oxygen/nitrogen (O2/N2) gas separation. Polysulfone (PSF) hollow fiber membranes were fabricated by phase inversion process using N,N-dimethylacetamide (DMAc) and tetrahydrofuran (THF) as co-solvent and ethanol as additive. The effects of bore fluid flow rate and polydimethysiloxane (PDMS) coating concentration on the separation characteristics of hollow fiber membranes were studied. Prior to gas permeation study, characterizations were performed to study the membrane morphology, its thickness and quality of PDMS coating layer on the membrane surface. It was found that the bore fluid flow rate played an important role for the O2/N2 separation as it could alter the membrane structure and dimension. The membrane fabricated with lower bore fluid flowrate exhibited better gas permeance and selectivity, owing to better structural integrity that favored the PDMS coating. The results indicated that the PSF hollow fiber membrane coated with optimum PDMS concentration could show greater O2/N2 gas permeability and selectivity relative to the PSF membrane without PDMS coating.