Facilitated transport membranes in the solid state have been attractive because they can improve both the permeability and the selectivity simultaneously to overcome the trade-off behavior. The carrier activity for facilitated transport plays a key role in determining separation performance. We have reported the solid-state facilitated transport membranes containing surface-activated Ag nanoparticles (NPs) as an olefin carrier for separation of olefin/paraffin mixtures, particularly propylene/propane mixture. Interestingly, the surface positive charge density of Ag atom in Ag NPs was linearly correlated with the propylene solubility and also with the propylene/propane selectivity. In addition, the separation performance has been maintained unchanged up to 500 hours.