The direct fluorination of polymers is a heterogeneous reaction using the mixture of F2 and inert gas. In general, the resulting fluorinated polymers have good barrier property chemical stability similar to those of the fluoro-polymers, and could be prepared from the simple process. In this study, the polysulfone dense films were surface fluorinated using the direct fluorination technique and gas permeability and selectivity of the prepared membranes were measured with varying both F2 concentration and reaction time. The introduction of F2 was confirmed by X-ray photoelectron spectroscopy(XPS), water contact angles, and atomic force microscopy(AFM). As the F2 increased, the permeability decreased while the selectivities for O2, CO2, and He gases relative to N2 increased.