We have investigated microscopic structures of sputter and pulsed laser deposited (PLD) anatase Nb-doped TiO2 transparent conducting films, and discuss what causes the degradation of resistivity in sputter-deposited films. Cross-sectional transmission electron microscope and polarized optical microscope images show inhomogeneous intragrain structures and small grains of similar to 10 mu m in sputter-deposited films. From comparison with PLD films, these results suggest that homogeneous film growth is the important factor to obtain highly conducting sputter-deposited film. (C) 2008 American Vacuum Society.