A series of monodisperse magnetic nanoparticles (NPs) MFe2O4 (M = Fe-II, M-II, Co-II, Zn-II) was synthesized through an improved sonohydrothermal method and then characterized for their structural properties. NaOH concentration and hydrothermal temperature were examined for their effects on the crystallization of MFe2O4 NPs. Thereafter, the synthesized NPs were applied to remove three commonly-used tetracyclines (TCs) from water, including tetracycline (TCN), oxytetracycline (OTC), and chlortetracycline (CTC). High removal efficiencies (>= 96%) were achieved for all the selected TCs within 5 mm. The adsorption kinetics of OTC on MFe2O4 NPs could be expressed well by the pseudo-second-order model. Based on the functional groups of TCs and the active surface sites of MFe2O4, the adsorption mechanisms were proposed. The used NPs could be regenerated easily by a methanol solution (60%, v/v) and recycled for the effective removal of TCs. This study demonstrates that the sonohydrothermal method is nontoxic, convenient and cost-effective for the synthesis of magnetic NPs which have potential applications in water treatment for removal of micro-pollutants. (C) 2013 Elsevier B.V. All rights reserved.