Highly selective capture of methane from nitrogen is considered to be a feasible approach to improve the heating value of methane and mitigate the effects of global warming. In this work, an ultramicroporous squarate-based metal-organic framework (MOF), [Co-3(C4O4)(2)(OH)(2)] (C4O42-=squarate), with enhanced negative oxygen binding sites was synthesized for the first time and used as adsorbent for efficient separation of methane and nitrogen. Adsorption performance of this material was evaluated by single-component adsorption isotherms and breakthrough experiments. Furthermore, density functional theory calculation was performed to gain the deep insight into the adsorption binding sites. Compared with the other state-of-the-art materials, this material exhibited the highest adsorption selectivity (8.5-12.5) of methane over nitrogen as well as the moderate volumetric uptake of methane (19.81cm(3)/cm(3)) under ambient condition. The unprecedented selectivity and chemical stability guaranteed this MOF as a candidate adsorbent to capture CH4 from N-2, especially for the unconventional natural gas upgrading. (c) 2018 American Institute of Chemical Engineers AIChE J, 64: 3681-3689, 2018