One of the effective techniques for improving separation properties of polymeric membranes is incorporation of suitable nanoparticles into their matrices. This study presents the preparation of three types of nanocomposite membranes comprising three grades of poly (ether-block-amide) (Pebax 1074, Pebax 1657 and Pebax 2533) and modified multi-walled carbon nanotubes (MWCNTs) with different loadings (1, 1.5, 2 and 2.5 wt%). The prepared membranes were characterized by field emission scanning electron microscopy (FESEM), attenuated total reflection-Fourier transfer infrared spectroscopy (ATR-FTIR) and X-ray diffraction (XRD). Permeation of CO2 and CH4 gases through the prepared membranes was measured at the pressure range of 2-8 bars and 25 °C. The results showed that the incorporation of MWCNTs into the polymers matrices improves CO2/CH4 selectivity. Further, Pebax 1074/MWCNT nanocomposite membrane exhibits better performance for CO2/CH4 separation compared to the neat Pebax and the two other nanocomposite membranes.