Plasticization behavior of polymeric membranes, in presence of a second component in the feed is different from plasticization of pure CO2 due to competitive sorption. This study focused on a mathematical model derived for permeation of mixed gases in glassy polymers considering the plasticization case. It was assumed that diffusion coefficient for all components were exclusively a function of plasticizing component. In this study, the partial immobilization model was employed to determine fraction of mobile sorbed gases. This model accurately predicted the permeation behavior of CO2 as plasticizer and N-2 in presence of plasticization. The model parameters were calculated by fitting experimental data from literature. Plasticization parameter (/3) decreased for both CO2 and N-2 by increasing fraction of N-2 in the feed. It means that plasticization of glassy polymers was suppressed. This decrease was caused by competitive sorption between CO2 and N-2. Indeed N-2 in the feed acts as an anti-plasticizer. In addition, permeances of the feed gas components were declined in comparison to pure gases, which might be attributed to reduction of sorption and occupying Langmuir sites with the second component. The proposed model is capable of giving a useful tool to enhance our knowledge related to permeability and selectivity behavior of mixed gas systems in glassy polymeric membranes. (C) 2015 Elsevier B.V. All rights reserved.