Porous magnetite (Fe3O4) secondary particles were prepared by a surfactant-free solvothermal method of up to 4 h. Fe3O4 secondary particles prepared for 3 h were about 300 nm in average diameter, composed of aggregated primary particles, and had a porous structure. Potential application of the Fe3O4 secondary particles as a drug delivery agent was evaluated by estimating their release of property. The amount of ibuprofen released was increased when an alternating current magnetic field (ACMF, 120 kHz and 7.8 kA/m) was applied to the prepared magnetite clusters in phosphate buffered saline (PBS) solution. Moreover, as-prepared samples dispersed in water well and exhibited quick magnetic separation with the help of an external magnetic field from a magnet. (C) 2016 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.