Nano-computed tomography (nanoCT) was used for non-invasive 3D visualization and characterization of porous gas diffusion layer (GDL) for polymer electrolyte membrane fuel cells (PEMFC). The study was conducted using reconstruction of 3D images of a GDL of polymer electrolyte fuel cell to determine the critical nanostructural parameters of the layer, such as porosity, mean pore radii, structure model index and degrees of anisotropy. Furthermore, permeability of the GDL was obtained through lattice Boltzmann numerical modeling.