BaBi4Ti4-5/4xNbxO15 (BBNTx, x = 0.0.05, 0.15, 0.30) ceramics have been prepared by solid state method. XRD data indicate the formation of single-phase-layered perovskites for all compositions. SEM micrographs suggest that the grain size decreases with Nb doping. The effect of niobium doping on the dielectric and relaxor behavior of BaBi4Ti4O15 ceramics was investigated in a wide range of temperatures (20-777 degrees C) and frequencies (1.21 kHz to 1 MHz). Nb doping influences T-c decrease as well as the decrease of dielectric permittivity at Curie temperature. At room temperature, undoped BaBi4Ti4O15 exhibits dielectric constant of similar to 204 at 100 kHz, that slightly increases with Nb doping. The conductivity of BBNT5 ceramics is found to be lower than that of other investigated compositions. The value of activation energy of sigma(DC) was found to be 0.89 eV, 1.01 eV, 0.93 eV and 0.71 eV for BBT, BBNT5, BBNT15 and BBNT30, respectively. (C) 2012 Elsevier Ltd. All rights reserved.