In order to study the influence of small amount of impurities on the copper oxidation kinetics, the oxidation was examined at 600–1050°C in 0.1 MPa oxygen atmosphere using 99.5% (2N) and 99.9999% (6N) pure copper specimens. The influence of impurities has been discussed considering the roles of the nonprotective CuO layer, the impurity layer at the Cu2O–Cu interface, and the diffusion of copper in the Cu2O layer. The nonprotective CuO layer for 2N copper can greatly enhance copper oxidation. However, the impurities concentrated at the region near the Cu2O–Cu interface for 2N copper can slow oxidation. Contrary to the presence of metallic impurities, such as Ni, Sb, and Pb, the nonmetallic elements As and Se dissolved in Cu2O have a deleterious influence on the outward diffusion of copper. Grain-boundary diffusion in Cu2O can somewhat contribute to 2N copper oxidation at 850–1050°C, but its effect in enhancing oxidation at 600–800°C is weaker than the effect of the impurity layer at the Cu2O–Cu interface in impeding oxidation.