In this paper, three novel silicon-containing polyimides (abbreviated as SiDA-TDA, SiDA-DDA and SiDA-BDA) were synthesized. The permeability to H-2, O2 and N2 of these polymer membranes was determined at 30-degrees-C and at 1 atm. The introduction of bis(phenylcarboxylic dianhydride)dimethylsilane (SiDA) into the backbone of polyimides appears to result in a significant increase in gas permeability, without a correspondingly large decrease in permselectivity. The relationships between chemical structure and permeability of polyimides were also discussed. Wide-angle X-ray diffraction measurements of the average segmental spacing of the membrane materials characterized the packing of the different polymer types.