We made study of the comparative characteristic of transparent organic light emitting diodes TOLEDs by using three kinds of a typical transparent conducting oxide (ITO (In₂O₃-SnO₂), IZO (In₂O₃-ZnO), AZO (ZnO-Al₂O₃)). The cathode used for transparent conducting oxide was prepared by rf magnetron sputtering at room temperature. We have carried out a systematic study of cathode preparation by sputtering with the aim of investigating, (1) resistivity and transmission of transparent conducting films, (2) morphology of films on organic films by AFM images, (3) electron injection for TOLED by using alkali metal (Cs). An electronic injection improved by doping Cs, and the decrease in driving voltage and in leaking current of TOLED and the improvement of luminance were observed.