The pore microstructures in two viscouse rayon-based ACF samples were characterized by nitrogen adsorption and HRTEM. For TEM, a two-dimensional fast Fourier transform (FFT) of the original TEM images was performed, and pores in different size ranges were extracted by the inverse FFT (IFFT) operation. The surface fractal dimensions of the samples were evaluated by using both N-2 adsorption and TEM image analysis. The results show that TEM can portray the shapes of the pore, and it can give a quantitative evaluation of surface irregularity that is consistent with nitrogen adsorption results.