The removal of ethane from ethene streams is of great importance and a challenging process for feedstock purification to produce polyethylene in the petrochemical industry. Traditional industrial cryogenic distillation is energy-intensive and expensive, while adsorptive separation technology using ethane selective adsorbents can effectively reduce this energy consumption. Herein, the direct functionalization of the open metal sites in a series of rare earth-based metal-organic frameworks (MOFs) [Ln-BTC (Ln(BTC)(H2O), Ln = Y, Sm, Eu, and Dy)] was achieved, which demonstrated highly efficient ethylene purification performance. A combination of single-component adsorption tests, ideal adsorption solution theory calculations, grand canonical Monte Carlo, and density-functional theory calculations showed that this series of MOFs selectively adsorbed ethane over ethylene. Therefore, these materials can be utilized as adsorbents for the efficient removal of low concentrations of ethane from an ethane/ethylene mixture to afford polymer-grade ethylene under ambient conditions.