The electrical conductivity of polycrystalline Li4/3Ti5/3O4 is reported between similar to 300 K and similar to 1000 K. Sintered and commercial pressed pellets were used for measurements. Impedance spectroscopy was applied (20 Hz-1 MHz) to determine the DC conductivity sigma(DC) and AC conductivity sigma(AC). Anomalies of sigma(DC) were observed at higher temperatures as a consequence of presumed order-disorder phase transitions, coupled to diffusion of Li+ between various spinel sites, as concluded in earlier work. There was a broad transitional region of sigma(DC) in this temperature range characterized by varying differential activation energies E-A. For sintered pellets, consisting of similar to 0.8-1.5 mu m grains, after run 1 up to similar to 960 K, E-A values were E-A similar to 0.80 eV above similar to 740 K and E-A similar to 0.57 eV below similar to 500 K for effective sigma(DC) deduced from the sum of bulk and grain boundary resistivities, while in the transitional temperature range the values were lower with the data taken under flowing N-2. Typically, sigma(DC)(500 K) similar to 10(-4)-10(-6) Omega(-1) cm(-1) and sigma(DC)(300 K) similar to 3 x 10(-10) Omega(-1) cm(-1); predominant conduction is due to ionic Li+ charge transport. For commercial similar to 0.1-0.3 mu m grain pellets, after run 1 up, the respective values were E-A similar to 0.87 eV above similar to 800 K and E-A similar to 0.61 eV between 495 K and 380 K. Below similar to 620 K, for both materials bulk sigma(DC) could be determined, which is a factor of 3-10 above the effective sigma(DC). For the frequency dependence of sigma(DC) of commercial Li4/3Ti5/3O4, a power law behaviour was established between 349 and 443 K. Applying DC voltage measurements, for sintered Li4/3Ti5/3O4 the electronic fraction of sigma(DC) was estimated to be < similar to 1% of the ionic fraction between 465 and 830 K. (C) 2010 Elsevier B.V. All rights reserved.