In this study, both the structural and gas permeation properties of mixed matrix asymmetric hollow fiber membranes were investigated. The average outer and inner diameters of the membranes are 1200 and 800 mu m respectively, and as used polymer was chosen the BTDA-TDI/MDI (P84) co-polyimide. Phenol-functionalized multi-wall carbon nanotubes were chosen as filler materials and their morphological characteristics were investigated by TEM. The membranes were then characterized by FTIR and SANS; Tg variations were evaluated by DSC measurements. The findings provide evidence for uniform dispersion of nanotubes and the existence of small structures formed by the filler addition. Finally, permeance experiments in a series of pure gases (He, H-2, CH4, N-2, O-2, C2H6, CO2 and C3H8) at 25, 60 and 100 degrees C were carried out. The results revealed that the good multi-wall carbon nanotubes dispersion leads to enhanced gas permeation properties. (C) 2014 Elsevier B.V. All rights reserved.