Lithium tracer diffusion experiments using neutron radiography (NR) technique were carried out on the perovskite-type structured lithium ion conductors La2/3-x,Li-3x,TiO3 in the temperature range from 150 to 400 degrees C. Isotope (Li-6) concentration profiles in the annealed samples consisting of Li-7 were measured by NR, from which the tracer diffusion coefficients of lithium ions were calculated. Lower lithium concentration samples showed higher diffusion coefficients and vice versa, which was consistent with the assumption that the diffusion coefficient is proportional to the cation vacancy concentration. On the other hand, the activation energies of lithium ion diffusion grow larger with the lithium content. In addition, correlation factors were discussed comparing with the diffusion coefficients obtained from the conductivity data. (c) 2005 Elsevier B.V. All rights reserved.