Recovery of heavier hydrocarbon gas (i.e. C3H8) from permanent gas (i.e. H2) during gas streams process is a great importance economically. Separation of H2/C3H8 gas using polysulfone (PSF) polymeric membrane was studied with the effect of post-treatment process such as annealing to improve the gas separation performance. PSF membrane annealed using a muffle furnace under vacuum conditions at 150°C for an hour. The result showed that annealing process caused a reduction in the mobility of the polymer chain, which was indicated by a shift of 2θ in XRD results. The cross-section morphology of membrane annealed at 150°C was examined by SEM. Annealing process of PSF membrane enhanced the H2/C3H8 selectivity by 619.77%, from 3.08 to 22.19. It was concluded that post-treatment PSF membrane could improve the H2/C3H8 separation performance compared to PSF membrane without annealing treatment.