An oxide thin film transistor, an array substrate, methods of manufacturing the same and a display device are disclosed. The oxide thin film transistor includes: a base substrate; and a gate electrode, a gate insulating layer, an oxide active layer, drain/source electrodes sequentially disposed on the base substrate. The oxide TFT transistor further includes an ultraviolet barrier layer disposed on the oxide active layer, the ultraviolet barrier layer is made of a resin material contains an ultraviolet absorbent. The stability of the oxide TFT is enhanced by disposing the ultraviolet barrier layer over the oxide active layer of the oxide TFT, since the ultraviolet barrier layer blocks the impact of UV light on the oxide TFT.