The nitride surfaces of uranium were prepared by the surface glow plasma nitriding (SGPN) and plasma immersion ion implantation (PIII) methods. The initial oxidation behaviors of modified surfaces were studied by X-ray photoelectron spectroscopy (XPS). The SGPN on the uranium surface led to a single layer of uranium sesquinitride (U2N3), while the PIII on the surface resulted in a compound layer composed of U2N3 and uranium dioxide (UO2). The oxygen covered on these modified layers led to the formation of UO2 from U2N3 and U2N3 from UN. The oxidized nitrogen species were also observed on the two types of nitriding layers, with the discussion of the N–O coaction behaviors.