This paper reports that the intergrowth ceramics Bi5TiNbWO15 (BW-BTN) have been prepared with the conventional solid-state reaction method. The dielectric and conductivity properties of samples were studied by using the dielectric relaxation and AC impedance spectroscopy in detail. Two distinct relaxation mechanisms were detected both in the plots of dielectric loss(tanδ) and the imaginary part (Z") versus frequency in the frequency range of 10 Hz-13 MHz. We attribute the higher frequency relaxation process to the hopping process of the oxygen vacancies inside the grains, while the other seems to be associated with the space charges bound at the grain boundary layers.The AC impedance spectroscopy indicates that the conductivities at 625 K for bulk and grain boundary are about 1.12×10-2 S/m and 1.43×10-3 S/m respectively. The accumulation of the space charges in the grain boundary layers induces a space charge potential of 0.52 eV.