The metal organic framework (MOF) is highly porous and has flexible structure. Through their intrinsic property, MOF can be used in the field of separation. There exists many kinds of MOF which show characteristic properties. In this work, Magnesium-MOF-74 (Mg-MOF-74) is used. The Mg-MOF-74 has one-dimensional channel with pore diameter near 1.1nm. Its pore size is too large to separate molecules in molecular scale. To tune the pore size of Mg-MOF-74, ligands are partitioned into the pore of MOF. 2,4,6-Tri(4-pyridyl)-1,3,5-triazine (tpt) can be partitioned into the pore of Mg-MOF-74, through the interaction between nitrogen atom of tpt ligand and open metal site of magnesium. We approached two types of ligand insertion method. The first one is As-synthesized Method (ASM). Through this method, tpt ligands are put at the initial stage of synthesis reaction. The second one is Post-synthesis Method (PSM). For this method, the ligands are inserted after the synthesis of pristine Mg-MOF-74. Ligand partitioned Mg-MOF-74 will be characterized through Powder X-ray Diffraction (PXRD) and Matrix-Assisted Laser Desorption Ionization. Also the adsorption isotherm data analysis are used to characterize the pore structure. In order to test the separation performance among methane (C1), ethane (C2) and propane (C3) gas, pressure decaying curve is obtained and analyzed through several apparatus. Diffusivity of C1, C2 and C3 gas will be calculated by Fickian diffusion model. Diffusion selectivity and sorption selectivity will be calculated based on the data.