The electrical measurements performed on Nb6VSb3O25-ceramics showed a sharp increase of the n-type electrical conduction at 330 K from the extrinsic region with the activation energy of E-a = 0.01 eV to the intrinsic one with the activation energy of E-a = 0.75 eV. At high temperatures, i.e. above 520 K, a rather well defined linear slope of diffusion thermopower was found which extrapolates to (0, 0). The I-V characteristics, measured at 300 and 400 K, showed a symmetric and non-linear behaviour as well as a broad minimum of the conductance G vs. the applied voltage V, which is being shifted into the higher voltages and simultaneously its value falls with a rise in temperature. These results are interpreted in a framework of deep donor and shallow trap levels as of grain boundaries. (C) 2013 Elsevier Ltd. All rights reserved.