Transparent conducting indium tin oxide (ITO) thin films were prepared on glass substrates by a magnetron sputter type negative ion source which requires cesium (Cs) vapor injection for surface negative ionization on the ITO target surface. Although the film was prepared at 70°C, it attained high optical transmittance, 88% and low resistivity, 2.03×10−4Ωcm, at an optimized Cs partial pressure of PCs=1.7×10−3Pa. The as-deposited ITO films have a poly-crystalline structure with (211), (222), (400), (411) and (440) reflections.Also, ITO films prepared at PCs=1.7×10−3Pa were post-deposition vacuum annealed at 300°C for 30min. The films had a resistivity of 1.8×10−4Ωcm and a transparency of 89.2%. The post-deposition vacuum annealed ITO film was used as an anode for a transparent organic light emitting diode (TOLED). A maximum luminance of 19,000cd/m2 was obtained.