In this paper, capabilities of carbon nanotube (CNT) membranes fabricated in cylindrical pores of anodic aluminum oxide (AAO) substrate to separate the binary mixtures of CH 4 /N 2 are studied experimentally. For this purpose, the permeability and selectivity of three CNT/AAO membranes with different growth time as 6h, 12h and 18h are investigated. CNTs are grown vertically through holes of AAO with average pore diameter of 45nm by chemical vapor deposition (CVD) of acetylene gas. CNT/AAO membranes with the same CNTs’ outer diameters and different inner diameters are synthesized. The AAO are characterized by SEM analysis. In addition, SEM, TEM, BET N 2 adsorption analysis and Raman spectroscopy are employed to characterize aligned CNTs. Study on permeability and selectivity of membranes for three binary mixtures of CH 4 /N 2 showed that when the CNT inner diameters are 34nm and 24nm, viscous flow is the governing mechanism and insignificant selectivities of 1.2–1.24 are achieved. However, the membrane with CNT inner diameter and wall thickness of 8nm and 16nm respectively is considerably selective for CH 4 over N 2 . It was also found that CH 4 mole fraction in the feed and upstream feed pressure have major effect on permeability and selectivity. The membrane with 18h synthesis time showed the selectivity is in the range of 1.8–3.85. The enhancement factor for N 2 single gas diffusivity was also found to be about three times larger than that predicted by Knudsen diffusion model.