The present invention relates to an organic/inorganic hybrid thin film passivation layer comprising an organic polymer passivation layer prepared by a UV/ozone curing process and an inorganic thin film passivation layer for blocking moisture and oxygen transmission of an organic electronic device fabricated on a substrate and improving gas barrier property of a plastic substrate; and a fabrication method thereof. Since the organic/inorganic hybrid thin film passivation layer of the present invention converts the surface polarity of an organic polymer passivation layer into hydrophilic by using the UV/ozone curing process, it can improve the adhesion strength between the passivation layer interfaces, increase the light transmission rate due to surface planarization of the organic polymer passivation layer, and enhance gas barrier property by effectively blocking moisture and oxygen transmission.