Oxidation kinetics and oxide structures of three polycrystalline copper grades at different temperatures were studied by analytical transmission electron microscopy (AEM) and atomic force microscopy (AFM). The copper samples were oxidized in air at 200 and 350 degrees C for 1-1,100 min. AEM and AFM studies indicated that alloying and increase of temperature, accelerated oxidation. At 200 degrees C local oxidation was observed in the unalloyed copper samples while a uniform oxide layer formed on the alloyed coppers. At 350 degrees C a uniform oxide layer formed on all copper samples. The oxide structure was nanocrystalline cubic Cu2O after all oxidation treatments at 200 degrees C and after 5 min oxidation at 350 degrees C. After 25 and 100 min oxidation at 350 degrees C the crystal size of copper oxide had grown and the oxide structure was monoclinic CuO.