Pebax (R)/CNTs (MWNTs, MWNTs-OH and MWNTs-NH2) and Pebax (R)/MWNTs-NH2/GTA mixed matrix membranes (MMMs) were prepared with solution-casting method. First, the effect of CNTs functionalization on the properties of Pebax (R)/CNTs MMMs was studied. The functionalization of CNTs promoted their dispersion in Pebax (R) matrix. The gas permeabilities of Pebax (R)/CNTs MMMs were enhanced with the addition of CNTs. And, the enhancement of gas permeabilities induced by CNTs was in the order of MWNTs-NH2 > MWNTs-OH > MWNTs. Then, Pebax (R)/MWNTs-NH2 MMMs were chosen to be further modified with GTA. GTA promoted the dispersion of MWNTs-NH2 in Pebax (R) matrix, and it acted as a plasticizer and increased the chain mobility of Pebax (R) as well as the FFV of Pebax (R)/MWNTs-NH2/GTA MMMs. The gas diffusion coefficients and solubility coefficients all increased with the increase of GTA content. Consequently, the gas permeabilities of Pebax (R)/MWNTs-NH2/GTA MMMs remarkably increased with the increase of GTA content. CO2 permeabililty of P10C(N)1G25 was higher than pristine Pebax (R) and P10C(N)1G0 by almost ten times and six times, respectively. CO2/light gas separation performance of Pebax (R) was significantly enhanced by CNTs and GTA. (C) 2016 Elsevier B.V. All rights reserved.