Mixed-matrix membranes (MMMs) comprised of polydimethylsiloxane (PDMS) as continuous and zeolite (ZSM-5) as dispersed phase have been prepared to investigate CO2 separation from gas mixtures, focusing on the high solubility of CO2 in ZSM-5/PDMS MMMs for separating CO2-N2 mixtures. ZSM-5 incorporation in PDMS significantly increases the permeability of single gases and a similar effect is observed for gas mixtures. Membrane performance is evaluated using the Maxwell model; an interphase gap between the filler and the polymeric phase is identified. A modified Maxwell model is applied to account for this additional transport through the membrane.