The conductivity of nanometer TiO2 thin films was presented in this paper. The dependence of the conductivity of TiO2 thin films on the thickness of the film and the substrate material were educed. The TiO2 films were deposited by reactive magnetron sputtering of a Ti targets in an Ar + O-2 mixture in a conventional sputtering reactor. The thickness of the films deposited on Ti varied in the range from 15 to 225 nm. The resistivity of the films was measured at room temperature in the air. It was found that the conductivity of TiO2 thin films varies in the range from conductor, semiconductor to nonconductor. This was attributed to electrons transfer at the interface between; the TiO2 and substrates, and the depth of electrons transfer was determined by the difference of work function. (C) 2003 Elsevier Science Ltd. All rights reserved.