Asymmetric polysulfone (PSF) membrane was developed by phase inversion in this study. Polysulfone (PSF) membrane was modified to develop a composite polymeric membrane. Polydimethyl siloxane (PDMS) was used to modify the PSF membrane. PDMS/PSF composite membrane was developed by dip coating of PDMS over PSF. Developed membranes were characterized in terms of membrane morphology by scanning electron microscope (SEM). Micro structure of polysulfone (PSF) membrane confirmed that developed membrane was asymmetric. Dense PDMS coating in microstructure of composite membrane was observed. Membrane swelling experiments were performed by immersing developed membranes in water for specific time period. PDMS/PSF composite membrane resisted water swelling as compared to PSF membrane. Performance of the membrane was evaluated before and after swelling within the pressure range of 2-10 bar. Reasonable decrement in permeance and selectivity was observed after membrane swelling. Thus, membrane swelling affected the separation performance of both PSF and PDMS/PSF composite membrane by decreasing the permeance and selectivity values. © Published under licence by IOP Publishing Ltd.