We demonstrate lithium insertion into brookite TiO2 in the nanophase regime. The extent of lithium insertion is significantly influenced by the crystallite size. A maximum of 0.95 Li/ TiO2 can be inserted into 10 nm size crystallites and the extent of lithium insertion is low (0.23 Li) in 33 nm crystallites. The reversibility decreases with an increase in crystallite size. The contrasting behavior of brookite and rutile TiO2 suggests that the structural features of brookite TiO2 may play an important role in determining Li insertion behavior. © 2008 The Electrochemical Society.