We have studied the oxidation kinetics of Cu and Cu3Ge thin films in air using in situ resistivity measurement and x-ray photoelectron spectroscopy. Thin films of Cu oxidize in air around 250°C to form CuO with an activation energy of 0.74 eV. In contrast to Cu, thin films of Cu 3Ge oxidize only above 450°C. The excellent oxidation resistance of Cu3Ge is due to the thin GeO2 layer which protects Cu3Ge from oxidation below 450°C. Above 510°C, GeO 2 evaporates and the oxidation protection is lost. Besides the excellent oxidation resistance and low resistivity, we also found Cu 3Ge to have a better adhesion to SiO2 than Cu. It has the potential to be used as an adhesion layer and passivation layer in Cu metallization.