Niobium-substituted Li4Ti5-xNbxO12 electrodes (0 <= x <= 0.25) have been synthesized by a solid-state method. The structure and electrochemical performance of these as prepared powders have been characterized by differential thermal analysis (DTA) and thermogravimetery (TG), X-ray diffraction (XRD), Raman spectroscopy (RS), scanning electron microscopy (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and the galvanostatic charge-discharge test. The XRD and RS results show that the Nb5+ can partially replace Ti4+ and Li+ in the spinel and there are very few oxygen vacancies in the Li4Ti4.95Nb0.05O12 with a higher electronic conductivity. The Nb-doped lithium titanium oxide samples show smaller particle size and more regular morphology structure, and Li4Ti4.95Nb0.05O12 has the highest initial discharge capacity and cycling performance among all the samples cycled between 0.0 and 2.0 V. CV implies that the niobium doping is beneficial to the reversible intercalation and deintercalation of Li+. EIS indicates that Li4Ti4.95Nb0.05O12 has a smaller charge transfer resistance corresponding to a much higher conductivity than that of Li4Ti5O12 corresponding to the extraction of Li+ ions. The superior cycling performance and wide discharge voltage range, as well as simple synthesis route and low synthesis cost of the Li4Ti4.95Nb0.05O12 are expected to show a potential commercial application. (C) 2011 The Electrochemical Society. [DOI:10.1149/1.3533391] All rights reserved.