This paper shows that copper, when in direct contact with lead (II) oxide, is subject to catastrophic oxidation at 800 °C in air. Isothermal kinetics of this oxidation were found to obey the parabolic rate law, which is evidence of diffusion limiting of the process. The calculated parabolic rate constant of copper oxidation is 5.3 × 10−5 and 7.2 × 10−5 kg2 m−4 s−1 at a specific PbO mass of 0.35 and 0.8 kg m−2, respectively, which are two orders of magnitude higher than the value of pure copper under the same conditions. This is due to higher (as compared to solid oxides) diffusion coefficients in the oxide melt contained in the oxide layer. The microstructure and the phase composition of the formed oxide layer were also investigated.