As　a　unique　subclass　of　metal-organic　frameworks　(MOFs),　MOFs　with　open　metal　site　(OMS)　are　demonstrated　efficient　gas　separation　performance　through　pi　complexation　with　unsaturated　hydrocarbons.　However,　their　practical　application　faces　the　challenge　of　humidity　that　causes　structure　degradation　and　completive　binding　at　the　OMS.　In　this　work,　the　effect　of　linker　methylation　of　a　copper　MOF　(BUT-155)　on　the　C2H2/CO2　separation　performance　under　humid　condition　is　evaluated.　The　water　adsorption　isotherm,　adsorption　kinetics,　and　breakthrough　under　dry　and　humid　conditions　are　performed.　The　BUT-155　with　methylated　linker　exhibits　lower　water　uptake　and　adsorption　kinetics　under　humid　condition　(RH　=　20%),　in　comparison　with　HKUST-1.　Therefore,　the　C2H2/CO2　separation　performance　of　BUT-155　is　much　less　affected　by　water,　especially　under　higher　gas　flow　rate.　Moreover,　the　dynamic　C2H2/CO2　separation　performance　of　BUT-155　can　maintain　five　breakthrough　cycles　under　humid　conditions　(RH　=　20%　and　RH　=　80%)　without　obvious　performance　degradation.　©　2024　The　Authors.　Advanced　Science　published　by　Wiley-VCH　GmbH.