Transparent organic light emitting diodes were developed by using a multilayer oxide as a composite cathode. The device structure is ITO/ MoO3(10nm) /NPB(60nm) / Alq3(65nm)/ Al(1nm)/MoO3(1nm)/ Al(Xnm) /MoO3(30nm).The composite cathode is MoO3/Al/ MoO3 (MAM). A thin Al layer (1nm) was introduced as an interlayer between the Alq3 electron transport layer and the MAM electrode. On the one hand

the thin Al improves the interface flatness between electrode and organic layers

while improving the conductivity of the electrode. On the other hand

electron injection was greatly improved by form an Ohmic contact between electron transport layer and a thin Al. Then we obtained the OLEDs optimum performance by changing the thickness of Al in MAM. In the thickness of 18nm about Al we can obtained the highest brightness is 2297cd/cm2.