A complex membrane of poly[(l-trimethylsilyl)-1-propyne]-graft-poly(acrylic acid)-Ag+ (PTMSP-g-AA-Ag+) was synthesized and characterized for C-4 olefin/paraffin gases separation. The 121.6% grafted PTMSP-g-AA-Ag+ complex membrane showed a homogeneous silver distribution across the membrane. Olefin could be transported across the complex membrane both by physical dissolution-diffusion phenomenon and by silver ion facilitated transport for subsequently forming the reversible (Ag-olefin)(+) complex. The permeation properties of C-4 gases, as measured by gas chromatography equipped with a gas permeability analyzer, indicated a facilitating effect for olefin. Typical selectivities of the 121.6% grafted complex membrane at 55 degrees C for the isobutene/isobutane and trans-2-butene/n-butane were 7.7 and 7.3, respectively. The effects of AA% grafting, measuring temperature and permanence stability on the permeability coefficients and separation factors were studied. The solubilities and diffusivities of C-4 gases as well as their selectivites were also examined.