This work reported on the fabrication of mixed matrix membranes by incorporating NH2-MIL-125 (Ti) nanofiller into 6FDA�durene polymer matrix for CO2/CH4 separation. The structural properties and morphology of the nanofillers and resultant membranes were investigated by X-ray diffraction, Brunauer Emmett and Teller, field emission scanning electron microscope, energy-dispersive X-ray spectroscopy mapping, thermogravimetric analysis and free fractional volume. The results showed that the CO2 and CH4 single gas permeability, as well as CO2/CH4 ideal selectivity were improved by incorporating NH2-MIL-125 (Ti) into the polymer matrix. Membrane loaded with 7.0 wt of NH2-MIL-125 (Ti) filler showed the highest CO2 permeability of 1115.70 Barrer and CO2/CH4 selectivity of 37.10, surpassing the 2008 Robeson upper bound. Furthermore, improvement of CO2 permeability of 119 and increment of 331 for gas pair selectivity in comparison with pure membrane were achieved. The results obtained in this work is due to the high porosity of nanofillers besides the attraction of amine functional group towards CO2. Overall, incorporation of amine-functionalized MIL-125 (Ti) nanofillers into 6FDA�durene polymer matrix has enhanced the separation performance of the membrane in CO2/CH4 separation. © 2020 Institution of Chemical Engineers