Spherical assembly composed of Mn3O4 nanoparticles with an average diameter of 400-600 nm have been prepared by a simple reactions between Ba(MnO4)2, H2SO4 and MnSO4 and thermal decomposition at 580 °C. The product was characterized by X-ray powder diffraction and scanning electron microscope. The adsorption performance of spherical assembly composed of Mn3O4 for alizarin red was investigated. The adsorbent showed high efficiency for the removal of alizarin red in water. The equilibrium of adsorption was achieved within 8 min. The isotherm adsorption data obeyed the Langmuir model, with a maximum adsorption capacity of 32.8 mg g-1.