This Letter focuses on the discovery of a transparent conducting oxide (TCO), anatase Ti1-xNbxO2 films with x=0.002-0.2. The resistivity of films with x >= 0.03 is 2-3x10(-4) Omega cm at room temperature. The carrier density of Ti1-xNbxO2 can be controlled in a range of 1x10(19) to 2x10(21) cm(-3). The internal transmittance for films with x <= 0.03 (40 nm thickness) is about 97% in the visible light region. The transport and optical parameters are comparable to those of typical TCOs, such as In2-xSnxO3 and ZnO. (c) 2005 American Institute of Physics.