The effect of alumina (Al2O3) nano-particles on gas separation properties of poly(4-methyl-1-pentyne) known as TPX was evaluated. Mixed matrix membranes (MMMs) were prepared with various weight percent (5, 10, 15, 20 and 30) of alumina nano-particles through solution casting along with solvent evaporation method. TPX and consequent MMMs were characterized using FT-IR, SEM and TGA methods. The MMMs permselectivities were determined through pure CO2 and CH4 permeation measurement and CO2/CH4 selectivity calculation. SEM images demonstrated the proper dispersion of alumina nano-particles in TPX matrix. Results from gas permeation showed that the permeability of both CO2 and CH4 as well as CO2/CH4 selectivities were increased with increasing alumina content. Significant increase of CO2 permeability (from 157.43 Barrer at 8 bar and no loading of Al2O3 to 527.78 Barrer at 8 bar and 30 wt% loading of Al2O3) and conspicuous enhancement of selectivity, from 7.73 to 12.51, were obtained in TPX MMMs.