The kinetics of the electrochemical lithium insertion reaction in nano-sized rutile TiO2 has been investigated using ac impedance spectroscopy. The experimental data are obtained for a rutile compound synthesized via a solution technique and characterized by a morphology corresponding to spherical particles made of a large number of very thin nanorods 20nm thick. The results are discussed as a function of the Li content x for 0< x ≤0.8 in Li x TiO2, the temperature over the range 10–50°C and the number of discharge–charge cycles. The significant linear decrease of the chemical diffusion coefficient D Li vs. the lithium content and the high values of D Li found in the composition range 0< x ≤0.5 are discussed and related with the electrochemical behaviour of the nano-sized material. From comparison with the bulk material, a promoting effect of the morphology on the kinetic characteristics is evidenced. For the first time an experimental evaluation of the activation energy for Li diffusion in nano-sized rutile TiO2 is obtained; the value of 0.35eV being much lower than that reported from computational experiments for the micro-sized oxide. This work also demonstrates a new system takes place from the second cycle, characterized by a significant improvement of Li diffusion by a factor five and allowing high rates to be used.