Niobium oxide coating was prepared on AZ31 magnesium alloy by RF sputtering and RF reactive sputtering. The microstructure, phase composition, chemical valence state, adhesion, and corrosion resistance of the coatings were studied by scanning electron microscope, X-ray diffractometer, X-ray photoelectron spectrometer, multifunctional material surface performance tester, and electrochemical workstation. The results show that both layers have an amorphous columnar structure, the niobium valence state of Nb5+, and excellent corrosion protection for AZ31 magnesium alloy up to 93% and above. Compared with RF sputtered niobium oxide coating, RF reactive sputtered niobium oxide coating has enhanced surface compactness, boosted corrosion resistance, and increased adhesion by about 7.4 times.