We have performed a comparative investigation of the series compounds (InSb)(n)Cu-m to assess the roles of Cu addition on the thermoelectric properties and nanostructuring in bulk InSb. Detailed temperature dependent transport properties including electrical conductivity, the Seebeck coefficient, and thermal conductivity are presented. The Seebeck coefficients of In20Sb20Cu (m:n = 1:20) are increased by 13 percent in magnitude if compared to those of InSb, which is responsible for the 22 percent enhancement in the highest ZT value at 687 K. Although the magnitudes of k(L) are larger than those of InSb over the entire temperature range, a remarkable reduction in lattice thermal conductivities (k(L)) was observed with measuring temperature elevation. Such changes are mainly due to the precipitation of a large number of Cu9In4 nanoparticles with the size of smaller than 5 nm, dispersed in the matrix observed using high resolution transmission electron microscopy (HRTEM) images. (C) 2011 Elsevier B.V. All rights reserved.