Mixed-matrix gas separation membranes were prepared by embedding various content of halloysite nanotubes (HNTs) (0, 0.5, 1, 1.5, and 2 wt%) within poly (ether-block-amide) matrix. XRD, FT-IR, TGA, and SEM analyses were conducted to study crystal structure, chemical bonds changes, thermal resistance, and cross-sectional morphology of the resultant membranes, respectively. Permeability values of pure CH4 and CO2 gases through the synthesized neat and mixed-matrix membranes (MMMs) were experimentally determined at constant temperature (25 °C) and several pressures (4, 6, 8, and 10 bar). The obtained results exhibited improved CO2 permeability of the MMMs comparing with the pristine Pebax membrane. As an example, at a pressure of 4 bar, raising the incorporated HNTs loading from 0 to 2wt% enhanced the permeability of CO2 from 76.50 to 101.23 Barrer.