Ba5BiNiNb9O30 ceramics with tetragonal tungsten bronze structure were prepared by a solid-state reaction process and their dielectric and magnetic properties were investigated. The dielectric constant peaks shift to higher temperatures and decrease in magnitude with increasing frequency. The dielectric relaxation follows the Vogel-Fulcher relation with E-a = 0.106 eV and T-f = 161.0 K. The temperature variation of the dielectric constant shows a diffuse phase transition having a diffusivity parameter value of 1.75 at 10 kHz. The diffuse ferroelectric transition can be attributed to the random distribution of Ni and Nb ions throughout the B sites and Ba and Bi at A1 sites of the tetragonal tungsten bronze structure. A negative paramagnetic temperature theta(Weiss) indicates the presence of weak antiferromagnetic interactions in Ba5BiNiNb9O30 ceramics. (C) 2011 Elsevier B.V. All rights reserved.