The transport properties of gases in mixed matrix membranes (MMMs) are important in materials design. Here, a novel time-dependent density functional theory (TDDFT) method to study the transport properties of gases in MMMs is developed. The MMM is modeled by inserting a spherical filler into the continuous polymer phase, which is similar to the Maxwell model; additionally, the inhomogeneity of the filler and the molecular correlations were taken into account in the TDDFT method. Transport properties such as permeation, density profile, flux, and chemical potential are examined and discussed. TDDFT prediction of the permeation is found to be higher than that of the Maxwell model, and the filler-polymer interface is key to tuning this effect, which also seems to be the dominating factor in the transport process on both the microscopic and macroscopic scale. (c) 2017 American Institute of Chemical Engineers AIChE J, 63: 4586-4594, 2017