Nb2O5 ceramic coatings were prepared on Ti6Al4V titanium alloy and AZ31 magnesium alloy by RF magnetron sputtering. The microstructure, residual stress, adhesion, and corrosion resistance of the coatings were studied. The results show that both layers are dense with uniform particles in size and no apparent defects as micro-cracks and holes. When the thickness of the Nb2O5 coating is 1.98 μm, the residual stress (27.1 MPa) of the coated Ti6Al4V sample is 65.1% lower than that of the coated AZ31 while the adhesion (9.24 N) is 13.2 times higher than that of the coated AZ31 sample. Nb2O5 ceramic coating can effectively enhance the corrosion resistance of Ti6Al4V and AZ31. However, the coated AZ31 sample is superior to the coated Ti6Al4V sample in decreasing corrosion current density, increasing polarization resistance, and protection efficiency.