In this contribution, we compare the adsorption capacity of different MFe2O4 (M = Mn, Fe, Co, Ni) ferrite nanocrystals synthesized by hydrothermal method for Congo red (CR). It is the first time to give a comprehensive comparison and analysis of the adsorption capacity of ferrite nanocrystals with spinet structure for CR. Research indicates that the cations distribution of MFe2O4 ferrites is the most important factor to decide their adsorption capacity. Electrostatic absorption was conceived as the main adsorption mechanism. Meanwhile, the MFe2O4 nanoparticles exhibited a clearly ferromagnetic behavior under applied magnetic field, which allowed their high-efficient magnetic separation from wastewater. Furthermore, acetone is an effective desorption agent for desorption of MFe2O4 nanoparticles loaded by CR. All of the spinel ferrite nanocrystals possess good soft-magnetism, especially. CoFe2O4 nanocrystals exhibit a higher saturation magnetization of 86.1 emu g(-1) as well as the outstanding adsorption capacity for CR. By the calculation of Langmuir isotherm model, the maximum adsorption capacity of CoFe2O4 for CR is 244.5 mg g(-1). (C) 2011 Elsevier B.V. All rights reserved.