The gas permeation properties of a new poly (dimethylsiloxane) (PDMS) membrane containing different concentrations of amino-hydroxy functionalized poly (dimethylsiloxane) have been measured for structure-property relationship. The corresponding cationic membranes were prepared by treating the amino-hydroxy functionalized poly (dimethylsiloxane) membranes with HBr gas. The functionalized siloxane materials were characterized by IR, H-1 and C-13 NMR, GPC, DSC and TGA techniques. The permeability of N-2, O-2, CH4 and CO2 were determined for different concentrations of non-ionic and cationic membranes. The permeability value was found to be decrease with increase in the amount amino-hydroxy functionalized siloxane. The permselectivity value for O-2/N-2 was found to be around 2.3 for both non-ionic and cationic membranes. However, significant increase in the permselectivity values of 4.12 and 5.6 were observed for CO2/CH4 system in the case of non-ionic and cationic amino-hydroxy functionalized siloxane membranes, respectively. A significant increase in the solubility of CO, with amino-hydroxy functionality especially in the case of cationic membrane was observed. (C) 2004 Elsevier B.V. All rights reserved.