The permeation properties of $O_2;and;N_2$ were measured for bromobisphenol A polysulfone(BPSf), bisphenol A trimethylsilylated polysulfone(TMSPSf) and their blend membrane to investigate the structure-properties relationships. BPSf shows relatively high permselectivity. It can be explained that the strong polarity of bromine in BPSf increases chain packing ability. In this case the distance of polymer chains is reduced by increasing of interchain interaction by induced dipole. TMSPSf shows relatively high permeability. The higher value of permeability coefficients for TMSPSf is due to the substitution of very bulky trimethylsilyl groups. The replacement of phenyl hydrogens of bisphenol A polysulfone(PSf) with trimethylsilyl groups results in higher fractional free volume(FFV). In this work, taking into account the complimentary features of BPSf and TMSPSf, BPSf/TMSPSf blend was prepared and the compatibility in mixing are examined. The BPSf/TMSPSf blend shows higher permeability than commercial PSf, with minimum loss of selectivity. The miscibility of the BPSf/TMSPSf blend is confirmed by the single glass transition temperature.