In this paper we have focused on the surface treatment and activation of membranes (73 AC and 82 V) with plasma discharge, and on the determination of their physicochemical properties. The surface morphology, wettability, zeta potential of pristine and plasma-treated membranes were tested and compared. Our study is focused on how plasma treatment may be used to tailor the membrane properties. The reactive plasma with functional groups can actively improve the interfacial properties (OH groups for hydrophilicity, NH2 groups for interaction with CO2) and increase separation efficiency of the membrane process. The surface morphology is also significantly affected in the case of membrane 82 V, and rather globular structures appeared on the surface of the plasma-exposed membrane. This change of morphology is also accompanied by a decrease of surface area difference, for both plasma-treated membranes 73 AC and 82 V. Membrane 82 V is more sensitive to the plasma treatment at both of the tested plasma power levels and exposure times. In all cases, the zeta potential changes due to the presence of polar groups on the surface. Plasma modification effects on wettability of both types of membranes revealed that water contact angles (CAs) of membranes 73 AC modified for short times (20 and 60 s) are lower than CM of the membranes 82 V modified under the same conditions. X-ray photoelectron spectroscopy demonstrated an increase in atomic oxygen concentration upon plasma treatment, which then gradually decreased as a function of time. When the composite membranes are exposed to water, the active layers of the membranes become dense and the transport no longer follows the Knudsen mechanism. These swollen membranes follow a solution-diffusion mechanism and the membranes are much more selective and less permeable for all the measured gases. The permeability reduction is much stronger for H-2 compared to CO2. The selectivity increases a lot, especially for the CO2/CH4 pair, from 0.3 up to 13.