The electrical resistivity and microstructure of nano-carbon materials, such as anisotropic coal tar pitch (pitch C) and polyparaphenylene (PPP), were investigated. The resistivity of the samples measured under applied pressure decreased as the packing density increased. The change ratio, rho/PD (resistivity/packing density), for pitch C was larger than that for well-known petroleum pitch (Ashland 240), and the resistivity value of the former was about 30% smaller than that of the latter at the highest packing density. The difference in the resistivity under pressure is thought to be caused not only by the contact resistance of the grains but also by the difference in the domain structure of the two kinds of samples. The packing density of PPP, which is a disordered carbon material, is scarcely changed by applied pressure. The resistivity of PPP was found to be affected strongly by the heat treatment temperature. (C) 2004 Elsevier B.V. All rights reserved.