Three kinds of mesoporous silica materials including SYSG (commercial silica gel), SBA-15, and KIT-6 are used as the carrier for supporting silver nitrate via incipient wetness impregnation method. The resultant materials Ag/SYSG, Ag/SBA-15, Ag/KIT-6 are characterized by low-temperature nitrogen adsorption/desorption, X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, and energy-dispersive X-ray spectroscopy and also are used as adsorbents for ethylene and ethane separation. It is found that both the surface area and the dispersion of Ag cations have significant influences on the separation performances. The surface modification by AgNO3 has the adsorption mechanism changed through eta-complexation, which is in contrast to the physical adsorption through van der Waals force that is usually dominated by the surface area. The loss of surface area weakens the physical adsorption of ethane, whereas the well-dispersed Ag cations could promote the adsorption of ethylene; therefore, the selectivity is improved. As a result, Ag/SBA-15 shows the best separation performances among the tested materials.