Purification of C2H4 from a ternary C2H2/C2H6/C2H4 mixture by one-step adsorption separation is of prime importance but challenging in the petrochemical industry; however, effective strategies to design high-performance adsorbents are lacking. We herein report for the first time the incorporation of Lewis basic sites into a C2H6-selective MOF, enabling efficient one-step production of polymer-grade C2H4 from ternary mixtures. Introduction of amino groups into highly stable C2H6-selective UiO-67 can not only partition large pores into smaller cagelike pockets to provide suitable pore confinement but also offer additional binding sites to simultaneously enhance C2H2 and C2H6 adsorption capacities over C2H4. The amino-functionalized UiO-67-(NH2)2 thus exhibits exceptionally high C2H2 and C2H6 uptakes as well as benchmark C2H2/C2H4 and C2H6/C2H4 selectivities, surpassing all of the C2H2/C2H6-selective materials reported so far. Theoretical calculations combined with in situ infrared spectroscopy indicate that the synergetic effect of suitable pore confinement and functional surfaces decorated with amino groups provides overall stronger multipoint van der Waals interactions with C2H2 and C2H6 over C2H4. The exceptional performance of UiO-67-(NH2)2 was evidenced by breakthrough experiments for C2H2/C2H6/C2H4 mixtures under dry and wet conditions, providing a remarkable C2H4 productivity of 0.55 mmol g-1 at ambient conditions.