Separation of a gas mixture achieved by the vacuum swing adsorption (VSA) technology is considered as an efficient and energy-saving method for Xe/Kr mixtures, but developing efficient and stable adsorbents remains challenging. Herein, we report an ultramicroporous metal-organic framework, namely, MIL-120 with a suitable pore size (5.4 angstrom x 4.7 angstrom), rich hydroxyl-decorated sites, and ultrahigh stability, which is capable of highly selective adsorption of xenon from krypton. Specifically, MIL-120 exhibits an excellent adsorption capacity of Xe up to 1.15 and 1.99 mmol g(-1) at 298 K under 0.1 bar and 1 bar, respectively, and outstanding ideal adsorbed solution theory selectivity of 9.6 for the Xe/Kr mixture, which is comparable to those of benchmark porous materials. The isosteric heat of adsorption (Q(st)) and density functional theory calculations further confirm the stronger interaction of the adsorbent toward Xe than Kr. Furthermore, the cycling breakthrough experiments, hydrothermal and acid-based stability tests, and VSA assessment comprehensively demonstrate that the MIL-120 is an efficient and potent adsorbent for Xe/Kr separation under industrial conditions.