Complex impedance analysis of polycrystalline Pb2Bi3LaTi5O18, prepared by a high-temperature solid-state reaction technique has been carried out. XRD analysis indicated the formation of a single-phase orthorhombic structure. Impedance plots were used as a tool to analyse the behaviour of the sample as a function of frequency and temperature. The bulk resistance has been observed to decrease with rise in temperature showing a typical negative temperature coefficient of resistance (NTCR) type behaviour like that of semiconductors. The ac impedance studies revealed the presence of grain boundary effect at 450 degrees C and showed polydispersive non Debye-type dielectric relaxation. The frequency dependent ac conductivity at different temperatures indicated that the conduction process is thermally activated process. The activation energy for bulk (0.67 eV) and grain boundary (0.73 eV) was estimated from the temperature variation of respective conductivities. (c) 2006 Springer Science + Business Media, Inc.