A carbon aerogel was prepared by carbonizing a resorcinol-formaldehyde polymer gel at 800 degrees C. Nitrogen adsorption shows the obtained carbon aerogel has both micropores (0.54 nm) and mesopores (2.14 nm). Matrimid mixed-matrix membranes containing the carbon aerogels were. successfully prepared and evaluated for the permeation of H-2, N-2, O-2, CH4, CO2, and gas mixtures. The ideal selectivity of H-2/N-2, CO2/CH4, and O-2/N-2 gas pairs increased from 79.6, 34.5, and 6.6 for pure Matrimid to 111, 47.8, and 9.1 at 20% loading, respectively. These results suggest that the polymer chains can penetrate the carbon mesopores to achieve good contact between the carbon aerogel and Matrimid, while the micropores may provide size and shape selectivity.