Molecular transport through membranes containing zeolite crystals and slit mesopores between them was examined by molecular dynamics simulations. The feasibility of fabrication of this type of membranes was recently demonstrated in Yoon [K. B. Yoon, Acc. Chem. Res. 40 (2007) 29]. Our results indicate that mesopores could be used to increase the overall flux through membranes under the conditions when almost all guest molecules diffuse in the zeolite at least part of the time needed to cross over the membrane. Diffusion in zeolite micropores is essential for achieving selectivity in separations. The results are of interest for understanding and optimization of mixed matrix membranes. (C) 2009 Elsevier B.V. All rights reserved.