Submicron copper microcrystal was synthesized by reducing Cu₂O with hydrazine hydrate as reducer in aqueous solution,and was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The shapes of copper microcrystal depend on additives. Cubic copper particles were observed when the inorganic salt containing Cl^-,such as NH₄Cl,NaCl,or KCl,was added into the reaction system. By combined use of NH₄Cl and polyvinylpyrrolidone (PVP),the proportion of cubic copper particle number exceeded 90%,and the particle size is 0.1-0.5μrn. While other inorganic salt without Cl^-,such as Na₂SO₄ or (NH₄)₂SO₄,had little effect on the shapes of the copper particles. The growth mechanism of metallic copper crystal in aqueous solution was analyzed. It is suggested that the formation of cubic copper crystals is ascribed to the selective adsorption of Cl^- on copper crystal (100) faces.