Spinel-type Cu-doped Mn3O4 microcrystals with various shapes were synthesized by hydrothermal method. The interrelation between the preparative conditions and the composition, structure, and morphology of the products were investigated using various analytical techniques, such as X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and thermal gravimetric analysis. Results revealed that the introduction of Cu2+ ions into the reaction system promoted the formation of single phase Cu-doped Mn3O4. A gradual shape evolution from polyhedron to octahedron occurred upon increasing the additive copper content. Complete decolorization of organic dye (methylene blue) aqueous solution was achieved by treating the dye with Cu-doped Mn3O4 in acidic media, which shows the possible application of doped Mn3O4 as effective reagents for the degradation of organic contaminants in water. (C) 2010 Elsevier Ltd. All rights reserved.