Water stable mixed-matrix membranes (MMMs) were developed to help control the global warming by capturing and sequestrating carbon dioxide (CO

2

) from post-combustion flue gas originated from burning of fossil fuels. MMMs of different compositions were prepared by doping glassy polymer Ultrason

®

S 6010 (US) with nanocrystals of zeolitic imidazolate frameworks (ZIF-300) in varying degrees. Solution-casting technique was used to fabricate various MMMs to optimize their CO

2

capturing performance from both dry and wet gases. The prepared composite membranes indicated enhanced filler-polymer interfacial adhesion

consistent distribution of nanofiller

and thermally established matrix configuration. CO

2

permeability of the membranes was enhanced as demonstrated by gas sorption and permeation experiments performed under both dry and wet conditions. As compared to neat Ultrason

®

membrane

CO

2

permeability of the composite membrane doped with 40 wt% ZIF-300 nanocrystals was increased by four times without disturbing CO

2

/N2 ideal selectivity. In contrast to majority of previously reporte

d membranes

key features of the fabricated MMMs include their structural stability under humid conditions coupled with better and unaffected gas separation performance.