The lithium ionic conductivity and electrochemical stability of perovskite La2/3-xLi3xTiO3 (LLTO) have been determined with AC impedance spectroscopy, cyclic voltammetry and galvanostatic cycling. Ionic conductivity of La0.55Li0.35TiO3 and La0.57Li0.29TiO3 pellets sintered from four different powders was measured in the temperature range from 30 to 110 degreesC. Bulk conductivity was found to be closely related to the calcination temperature of the powders. Pellets from 1100 degreesC-calcined powders had higher bulk conductivity than from 1200 degreesC-calcined powders. The grain-boundary conductivity was mainly determined by the sample composition. The activation energies were 0.14-0.18 eV for bulk conduction and 0.41-0.43 eV for grain-boundary conduction. Lithium was intercalated into LLTO below about 1.8 V vs. Li. With addition of acetylene black, about 0.48 Li was reversibly inserted into and extracted out of La0.55Li0.35TiO3. A phase transition is proposed to take place during the lithium insertion. Published by Elsevier Science B.V.