In this study, epoxy-based nanocomposites containing multi-wall carbon nanotubes (CNTs) were produced by a calendering approach. The electrical conductivities of these composites were investigated as a function of CNT content. The conductivity was found to obey a percolation-like power law with a percolation threshold below 0.05 vol.%. The electrical conductivity of the neat epoxy resin could be enhanced by nine orders of magnitude, with the addition of only 0.6 vol.% CNTs, suggesting the formation of a well-conducting network by the CNTs throughout the insulating polymer matrix. To characterize the dispersion and the morphology of CNTs in epoxy matrix, different microscopic techniques were applied to characterize the dispersion and the morphology of CNTs in epoxy matrix, such as atomic force microscopy, transmission electron microscopy, and scanning electron microscopy (SEM). In particular, the charge contrast imaging in SEM allows a visualization of the overall distribution of CNTs at a micro-scale, as well as the identification of CNT bundles at a nano-scale. On the basis of microscopic investigation, the electrical conduction mechanism of CNT/epoxy composites is discussed.