Anatase type TiO2 has been previously largely reported as a candidate negative electrode material for lithium-ion batteries. We report here for the first time the complete in situ Raman study of lithium insertion and de-insertion into three variously nano-sized TiO2 anatase powders (Prolabo, ca. 80 nm. AK1, ca. 15 nm and MTi5 ca. 8 nm), of which AK1 and MTi5 show superior capacity and cyclability. From these measurements realized in a galvanostatic mode between 3 and 1 V versus Li/Li+, the phase transition from a tetragonal to an orthorhombic structure was clearly observed to take place at different quantities of x in LixTiO2. These results confirm the extension of the solid solution domain as particle size is reduced. For the smaller TiO2 nano-sized materials (AK1 and MTi5), a more pronounced decrease in band intensity when x > 0.3 for LixTiO2, was observed and may be related to the decrease in the optical skin depth linked to the conductivity increase as lithiation proceeds. (c) 2007 Elsevier Ltd. All rights reserved.