Niobium-doped ZnO transparent conductive films are deposited on glass substrates by radio frequency sputtering at 300A degrees C. The influence of O-2/Ar ratio on the structural, electrical and optical properties of the as-deposited films is investigated by X-ray diffraction, Hall measurement and optical transmission spectroscopy. The lowest resistivity of 4.0x10(-4) Omega A center dot cm is obtained from the film deposited at the O-2/Ar ratio of 1/12. The average optical transmittance of the films is over 90%.