A novel dry complex membrane, poly[(1-trimethylsilyl)-1-propyne]-AgClO4 (PTMSP-AgClO4), was prepared for C-4 olefin/paraffin separation. infrared spectra indicates that Ag(I) ions are complexed onto the unsaturated PTMSP main-chains. The olefin/paraffin separation factor could be enhanced by forming the reversible (Ag-olefin)(+) complex. For isobutene/isobutane separation, a typical ideal separation factor of 5.6 was obtained for a 32.7 wt% PTMSP-AgClO4 complex membrane. Gas transport in PTMSP and PTMSP-AgClO4 membranes show negative E(p) values due to their large negative value of Delta H-s. The isobutene’s solubility coefficient is greatly increased in the PTMSP-AgClO4 membrane. The gas permeation properties of isobutene/isobutane gases in PTMSP and PTMSP-AgClO4 membranes were studied. Dual-mode behaviors of the sorption of gases in PTMSP and PTMSP-AgClO4 membranes are also discussed.