A porous and thermally stable metal organic framework (MOF) of yttrium and 1,3,5-benzenetricarboxylate was synthesized, which belongs to the family of lanthanide-based MOF-76. Mixed-matrix membranes were developed by incorporating MOF-76 yttrium nanocrystals into Matrimid® 5218. The structure, composition, and morphology of synthesized lanthanide-based MOF-76 yttrium nanocrystals and mixed-matrix membranes were characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, and thermogravimetric analysis. The characterizations and gas permeation results of the prepared mixed-matrix membranes confirmed better adhesion and distribution of filler particles in the polymer. The results demonstrated that the addition of MOF-76 yttrium nanocrystals to the polymer matrix improved both the gas selectivity and permeability of mixed-matrix membranes compared to pure Matrimid membranes. Permeability of CO2 increased from 7.24 to 27.29 Barrer by increasing the particle content from 0 to 30 in pure gas experiments. Whereas with 30 wt concentration of MOF-76(Y) at 50:50 feed compositions, the selectivity increased for CO2/CH4 and CO2/N2 was 67 and 68, respectively. The rise in temperature from 298 to 338 K decreased the ideal selectivity up to 25 for both gas pairs due to polymer chain relaxations at elevated temperatures. The commercial importance of membranes was evaluated at different feed compositions and operating temperatures. © The Author(s) 2019.