The objective of this research is to investigate the effect of adding graphite nanoplatelet (GNP) particles into polyether imide film. Extruded films were produced with various amounts of GNP and different degrees of post-extrusion stretching. A uniform high degree of alignment of the GNP particles along both machine direction (stretching) and transverse direction was obtained under high stretching ratios. Tensile properties including tensile modulus, strength and elongation were investigated. O-2 permeability was reduced with the increase of GNP loading and stretching ratio of the film. The Bharadwaj model was applied to predict the permeability. Information of degree of alignment was obtained through analyzing SEM images in image-processing software and used with the Bharadwaj model, resulting in good agreement with experimental data. Annealing of the stretched films under 340 degrees C showed a significant improvement of both electrical and thermal conductivity in the film direction. Published by Elsevier B.V.