Electrodeposition of Cu2+ ion resulted in the growth of Cu2O single-crystal particles on an amorphous carbon electrode in solution. Cu2O single crystals grow at potentials higher than -0.55 V vs. saturated calomel electrode (SCE) in CsClO4 (pH 7) as well as H2SO4 (pH 2.0) and HCl (pH 2.1) solutions. However, Cu2O as well as Cu particles are formed simultaneously at potentials below -0.55 V vs. SCE. The oxygen in the Cu2O may come from water via cuprous hydroxide intermediate. The effect of anions on the crystal habit of the Cu2O particles was investigated by changing anions. Hexahedral Cu2O single-crystal particles were preferentially formed in CsClO4 solution, but in the presence of sulfate ion the Cu2O particles grow in a polyhedral form. Y-shape particles of Cu2O were obtained in the presence of chloride ion, which may be due to the effect of stronger adsorption of Cl- on the surface of growing particles. Number density and average size of the particles grown on the electrode vs. the kind of anions and electrodeposition potential are discussed.