This study investigates the effect of linker methylation on the C₂H₂/CO₂ separation performance of a copper metal-organic framework (MOF) named BUT-155 under humid conditions. The methylation of the linker in BUT-155 enhances its hydrophobicity, reducing water uptake and adsorption kinetics compared to HKUST-1. This improvement allows BUT-155 to maintain better separation performance under humid conditions, with a dynamic C₂H₂/CO₂ separation capacity of 76.4 cm³ g⁻¹ at 298 K and 1 bar. Under 20% relative humidity (RH), BUT-155 can maintain five breakthrough cycles without significant performance degradation, while HKUST-1 shows a 45% reduction in dynamic C₂H₂ capacity after five cycles. The study demonstrates that linker methylation is an effective strategy to enhance the hydrophobicity of MOFs with open metal sites, making them suitable for gas separation applications under humid conditions.This study investigates the effect of linker methylation on the C₂H₂/CO₂ separation performance of a copper metal-organic framework (MOF) named BUT-155 under humid conditions. The methylation of the linker in BUT-155 enhances its hydrophobicity, reducing water uptake and adsorption kinetics compared to HKUST-1. This improvement allows BUT-155 to maintain better separation performance under humid conditions, with a dynamic C₂H₂/CO₂ separation capacity of 76.4 cm³ g⁻¹ at 298 K and 1 bar. Under 20% relative humidity (RH), BUT-155 can maintain five breakthrough cycles without significant performance degradation, while HKUST-1 shows a 45% reduction in dynamic C₂H₂ capacity after five cycles. The study demonstrates that linker methylation is an effective strategy to enhance the hydrophobicity of MOFs with open metal sites, making them suitable for gas separation applications under humid conditions.