Surface of copper is easily oxidized and the resulting oxidation products cause an increase of the electric resistance which severely limits their applications. In this study, we tried to improve the electric conductivity of copper metal by replacement of the copper oxide with the copper bromide. As a result, we found that an increase of the concentration of cyclohexylamine hydrobromide (CHAB) used for bromination made it possible to keep a high electric conductivity of copper. Moreover, under the low CHAB concentration, suppress of the surface oxidation involved water content in the reaction media, which indicates that water influences the hold of copper bromide on the surface. Heat treatment accelerates the oxidation, however, for the brominated copper, decrease in the electric conductivity hardly observed even after the heat treatment at 100℃ for 4 h. These results show that the brominated copper on surface gives the oxidation resistance and the hold of copper bromide is influenced by the water content in the reaction media.