Mixed matrix membranes (MMMs) composed of polyimide Matrimid (R) and mesoporous silica spheres (MSSs) are prepared, characterized and tested in gas separation of equimolar mixtures H(2)/CH(4) and CO(2)/N(2) at different temperatures. Their performance is compared with MMMs using other glassy polymer: polysulfone Udel (R). The convenience of removing the structural agent from the pores and activating the mesoporous with calcination or chemical extraction has been studied. In both studied polymers, the permeability of the selective gas increases with the filler and the selectivity has a maximum at 8 wt% filler loading. These improvements are related to the mesoporosity of the filler, good interaction between the filler and the polymer, and change in the polymer structure as indicated in the characterization done by thermogravimetric analysis, X-ray diffraction, differential scanning calorimetry, and scanning and transmission electron microscopy. (C) 2010 Elsevier B.V. All rights reserved.