Intercalation of lithium ions in nanoporous anatase TiO2 was studied with XPS using a novel electrochem. prepn. technique. The electrolyte was 0.5 M LiClO4 in acetonitrile (not water-free). The electrochem. insertion of lithium ions creates reduced Ti ions (Ti3+), which was obsd. as a new well-resolved state in the Ti 2p core level spectrum shifted 2.1 eV to lower binding energy. The new Ti 2p state was reversible when the electrode was deintercalated. Changes in the O 1s core spectra were also obsd. and discussed in terms of hydrated lithium ions in the Helmholtz layer, or formation of Li2O/LiOH.