Removal of C2H4 from a CO2 stream is very important in ultrapurification of CO2 for its application and utilization. However, it is difficult to remove C2H4 completely from a CO2 stream via conventional cryogenic distillation because the volatility of C2H4 is similar to that of CO2. Another choice is the catalytic combustion method, but it is an energy-inefficient process, especially when it is coupled with the cryogenic distillation. Selective adsorption for removing C2H4 might be a promising alternative. A great effort has been made in C2H4/C2H6 separation and recovery of C2H4. There were, however, few reports about the removal of a trace amount of C2H4 from a CO2 stream. In this study, the AgNO3-modified NaY and HY zeolites are prepared and their adsorption performances are evaluated via a series of experiments of fixed-bed adsorption, frontal chromatographic adsorption, and temperature-programmed desorption (TPD). The structure of the sliver salt after being impregnated onto the supports has been characterized by thermogravimetric/differential thermal analysis, X-ray diffraction, and transmission electron microscopy. The experimental results show that both NaY and HY have poor adsorption selectivities of C2H4 from the C2H4/CO2 stream because of a stronger competition of CO2 with C2H4 for the physical adsorption sites, and AgNO3/NaY and AgNO3/HY, favored by their strong chemical adsorption sites, Ag ions, are able to remove C2H4 from the CO2 stream effectively.