Mixed matrix membranes (MMMs) were developed by adding MIL-125(Ti) and the amine-functionalized counterpart as fillers to Matrimid((R)) polyimide. Through a well-optimized synthesis, strong performing MMMs with loadings up to 30 wt% could be prepared. SEM images of the synthesized MMMs confirmed the good adhesion to and dispersion of the fillers within the polymer matrix. Significantly improved CO2 mixed gas selectivities and permeabilities for (50:50) CO2:N-2 and CO2:CH4 gas mixtures at 9 bar and 308 K were achieved. The separation results demonstrated that the overall separation efficiency is increased by the addition of both MIL-125 and NH2-MIL-125 fillers but that the NH2-functionalized filler is preferred as it leads to higher selectivities and permeabilities. The performance of the membranes was compared to previously reported literature data for (CO2:CH4) separation which shows that carefully tuned membrane synthesis procedure along with right selection of polymer and filler are crucial factors to get a highly selective and permeable membrane. Among non-fluorinated polymers forming the membrane matrix, present data outperform all previously reported MMM separation. MMMs based on fluorinated polyimide showed slightly higher selectivities, but much lower permeabilities. (C) 2015 Elsevier B.V. All rights reserved.