Polyhedral oligomeric silsesquioxane (POSS) is a promising nanofiller with a cubic inorganic framework and optional organic functional groups. In this work, organosilica-POSS mixed matrix membranes were successfully prepared via the incorporation of octabenzamidopropyl-POSS into 1,2-bis(triethoxysilyl)ethane (BTESE)-derived matrix for gas separation. The BTESE-POSS composites showed stable structures up to 400 degrees C, and the POSS could be loaded within a wide range of contents by adjusting the concentrations in mixed solutions. In the gas separation, the effects of POSS content and operating temperature were investigated. As POSS content increased, the selectivities for H-2/N-2 were enhanced. The highest H-2/N-2 selectivity of 52.1 was obtained for BTESE-POSS (50.0%) composite membrane, which amounted to an increase of 160% over that of pure BTESE membrane at 100 degrees C. The apparent activation energy for gas permeation through these composite membranes became higher than that of pure BTESE membrane, which indicated a smaller pore size obtained by the addition of POSS. The permeances of He and H-2 for BTESE-POSS mixed matrix membranes were well predicted by the n = 1 Maxwell-Wagner-Sillar model, suggesting that small gases permeated a stack of oblate ellipsoidal layers of these membranes with parallel transport to the pressure gradient.