Ca Nd Cu Ti O (x = 0, 0.1, 0.2) ceramics were prepared by a solid state reaction process, and single-phased structures were obtained for all the compositions. The dielectric characteristics of pure and Nd-substituted CaCu Ti O ceramics were investigated together with the microstructures. The mixed-valent structures of Cu /Cu and Ti /Ti in the present ceramics were confirmed by X-ray photoelectron analysis. The dielectric relaxation in the low temperature range was examined in detail and the variation of dielectric constant and dielectric loss was attributed to the modification mixed-valent structures. © 2010 Springer Science+Business Media, LLC.