Al₂O₃/Cu composites were prepared by internal oxidation of Cu-Al sheet at 900 ℃ to investigate the microstructure and properties of the composites, in which the Cu₂O powder was used as oxidizer. The results indicate that the Al₂O₃ particles are dispersively distributed in the diffusion zone. The grain size in surface and inner of diffusion zone is sharply different, finer in the surface than in the inner. The micro-hardness of surface of diffusion zone can be improved due to Al₂O₃ disperoids strengthening Cu matrix. Compared with solid soluted Al atom in Cu matrix, the Al₂O₃ disperoids has slightly affected the electron diffraction, resulting in the increase of electric conductivity after Al₂O₃ precipitation. With increase of deformation rate of Al₂O₃/Cu sheet in case of cold working, the tangle of Al₂O₃ disperoids with dislocation becomes worse and worse.