Selective adsorption of trace amounts of C₂H₆ from bulk C₂H₄ is a significantly important and extremely challenging task in industry, which requires an adsorbent with specific pore properties. Herein, we describe a strategy for adjusting the pore environment of metal–organic frameworks (MOFs) by introducing different amounts of methyl groups in the channel to enhance the guest–host interaction between C₂H₆ and the framework. To prove this concept, 2,3,5,6-tetramethylterephthalic acid (TMBDC) was deliberately added to a microporous MOF, Ni(BDC)(DABCO)_0.5, affording a series of mixed-ligand materials, Ni(BDC)_1−x(TMBDC)_x(DABCO)_0.5 (x = 0, 0.2, 0.45, 0.71, 1), having different pore environments. Significantly, these mixed-ligand materials demonstrated improved performance in terms of the adsorption capacity of C₂H₆ and C₂H₄ with an unprecedented C₂H₆ uptake of 2.21 mmol g⁻¹ for Ni(TMBDC)(DABCO)_0.5 at 0.0625 bar and 298 K. With the best theoretical C₂H₆/C₂H₄ selectivity predicted by IAST, Ni(TMBDC)(DABCO)_0.5 exhibited effective separation of C₂H₆/C₂H₄ (1/15, v/v) and great recyclability in five consecutive adsorption/desorption cycles throughout the breakthrough experiment.