The partial positive charge density of the surface of Ag nanoparticles was modulated by an electron acceptor, 7,7,8,8-tetracyanoquinodimethane (TCNQ), to improve their reversible interactions with olefins such as propylene, but not with paraffin. The silver binding energy in Ag NPs, representing the surface charge density, exhibited a maximum at a TCNQ concentration of 0.05 mol% (0.26 molecules per nm2). The amount of propylene adsorbed on the surface of the Ag NPs was strongly correlated with the silver binding energy with a high correlation factor of 0.97. In addition propylenes were found to be adsorbed on the TCNQ-uncovered, vacant sites of Ag NPs according to quantum mechanical calculation. It was therefore concluded that the enhanced interaction between the surface-modulated Ag NPs and propylene is attributable to the high separation performance for olefin-paraffin mixtures based on selective facilitated olefin transport.