This study investigates the separation of acetylene (C₂H₂) from carbon dioxide (CO₂) under humid conditions using a methylated copper metal-organic framework (MOF), BUT-155. The research addresses the challenge of humidity affecting MOFs with open metal sites (OMS), which can cause structural degradation and competitive binding. The methylated linker in BUT-155 enhances its hydrophobicity, reducing water adsorption and improving the separation performance of C₂H₂ over CO₂. The MOF exhibits high C₂H₂ adsorption capacity (145.1 cm³ g⁻¹ at 298 K and 1 bar) and selectivity (6.43 at 298 K and 1 bar). Under humid conditions (RH = 20% and 80%), BUT-155 maintains five breakthrough cycles without significant performance degradation, demonstrating its stability and recyclability. The dynamic separation capacity of BUT-155 under humid conditions is 65.3 cm³ g⁻¹, which is 85.5% of the dry gas capacity. In contrast, HKUST-1 shows a significant decrease in performance under humid conditions. The study highlights that linker alkylation is an effective strategy to enhance the hydrophobicity of MOFs with OMS, enabling their use in gas separation under humid conditions. The results demonstrate that the adverse effects of water can be significantly reduced through linker modification, thus improving the separation performance of MOFs in practical applications.This study investigates the separation of acetylene (C₂H₂) from carbon dioxide (CO₂) under humid conditions using a methylated copper metal-organic framework (MOF), BUT-155. The research addresses the challenge of humidity affecting MOFs with open metal sites (OMS), which can cause structural degradation and competitive binding. The methylated linker in BUT-155 enhances its hydrophobicity, reducing water adsorption and improving the separation performance of C₂H₂ over CO₂. The MOF exhibits high C₂H₂ adsorption capacity (145.1 cm³ g⁻¹ at 298 K and 1 bar) and selectivity (6.43 at 298 K and 1 bar). Under humid conditions (RH = 20% and 80%), BUT-155 maintains five breakthrough cycles without significant performance degradation, demonstrating its stability and recyclability. The dynamic separation capacity of BUT-155 under humid conditions is 65.3 cm³ g⁻¹, which is 85.5% of the dry gas capacity. In contrast, HKUST-1 shows a significant decrease in performance under humid conditions. The study highlights that linker alkylation is an effective strategy to enhance the hydrophobicity of MOFs with OMS, enabling their use in gas separation under humid conditions. The results demonstrate that the adverse effects of water can be significantly reduced through linker modification, thus improving the separation performance of MOFs in practical applications.