At present, the dominant technology for olefin/paraffin separations is cryogenic distillation, which is extremely energy-intensive. Developing advanced adsorbent materials would be a first step toward cost-effective alternatives such as pressure swing adsorption or temperature swing adsorption. In this work, we report a silver-decorated hafnium metal organic framework, NUS-6(Hf)-Ag, as a C2H4-selective adsorbent for C,H-4/C2H6 separation. NUS-6(Hf)-Ag was synthesized by the modulated hydrothermal approach followed by ion-exchange reactions. The successful introduction of Ag(I), confirmed by X-ray photoelectron spectroscopy and energy-dispersive spectroscopy, increased the ideal C2H4/C2H6 selectivity of the resultant NUS-6(Hf)-Ag material to 6, which was 5 times that of NUS-6(Hf). Breakthrough experiments further confirmed the C2H4/C2H6 separation performance of NUS-6(Hf)-Ag, indicating coadsorption C2H4/C2H6 selectivities greater than 3. In addition, NUS-6(Hf)-Ag was found to maintain its crystallinity and the oxidation state of Ag(I) after recyclability tests. This study clearly demonstrates the promising potential of Ag-decorated metal organic frameworks as adsorbent materials in adsorption-based C2H4/C2H6 separations.