The purpose of this study is to develop new transparent conducting oxide (TCO) films by using combinatorial approach and to apply them for organic light emitting diodes (OLED) and/or thin film photovoltaic devices. For this, we have explored several TCO films with multi-components and optimized their properties by employing combinatorial sputtering system. For the first, we have fabricated combinatorial libraries composed Zn-In-Sn-O (ZITO) to reduce In content comparing with Sn-doped indium oxide (ITO). The ZITO films showed amorphous structure at the substrate temperature ranged RT∼ 350 °C, high transmittance over 85% at the visible range wavelength, and resistivity as low as 3x10-4∼10-3Ωcm. These results reveal that the ZITO films have indium composition as low as 30∼40% comparing with equivalent ITO films. Furthermore, we have fabricated OLED on glass substrates by using the amorphous ZITO anode. OLED fabricated on amorphous ZITO-coated glasses have exhibited good characteristics comparable to OLED on ITO films. Besides OLED, the amorphous ZITO TCO can be applied for other optoelectronic devices like electronic paper, thin film photovoltaic, and smart window.