For the longevity of OLEDs, passivation of OLEDs is an important process step since organic materials used in OLEDs are very vulnerable to moisture. In this work, the passivation effect of the plasma polymerized para-xylene (PP$ ho$X) layers was studied. The PPpX layers deposited by PECVD were formed on top of the cathode with various plasma powers of 50 - 90 W. Passivation effect of PP$ ho$X was significantly dependent upon the deposition plasma power of the PP$ ho$X film. The lifetime of OLEDs with the 70 W deposited PP$ ho$X passivation layer was about 5 times longer than that of the control device.