In the present study, the gas permeation properties of carbon molecular sieve (CMS) membranes dispersed with palladium nano particles via supercritical CO2 impregnation method were investigated. The palladium nano particles located near the permeation path consisting of slit-like micropore mouth were shown to function mainly as a selective permeation barrier, resulting in the excellent permselectivity for H-2/N-2 gas pairs.