The K-doped Y2/3Cu3Ti4O12 system was prepared and investigated. K doping is of great benefit to the growth of the grain size. Proper amount of K substitution in Y2/3Cu3Ti4O12 ceramics makes the dielectric loss significantly decreased. Very large epsilon(r) of similar to 1.1 x 10(4) and relatively low tan delta of similar to 2.6% are simultaneously observed for the samples with x = 0.020 and 0.035 when measured at similar to 10 kHz. The lowered dielectric loss is closely associated with the enhanced localized behavior of conduction process at grain boundary. The dielectric relaxation behaviors of grain boundary become much more difficult after K doping. Impedance analysis suggests that the same entities are responsible for the conduction and dielectric relaxation behaviors of grain boundary. Scaling behaviors indicate that the physical nature of their dielectric relaxation and conduction behavior are independent of the measurement temperature. (C) 2015 Elsevier B.V. All rights reserved.